This is simple and easy. You will find a quick example here: How-to.
For a better integration, you can also directly use the tiles at http://tiles.opensnowmap.org/pistes/{z}/{x}/{y}.png with your favorite map library, like OpenLayers or Leaflet.
Don’t forget to give a proper attribution to Openstreetmap !
Yves
Update 2020: Tile url changed
Simply the pistes added in the openstreetmap database every year until now,2014 update.
Openstreetmap ski map is still the most comprehensive ski map world-wide. On28.12.2014, 79665 km of ski trails on the map.
Yves
Ski lifts names are now displayed on OpenSnowMap.
This wasn’t done until now because I was unable to place the name labels exactly at the same place than on OpenStreetMap background map. The rendering of ski lifts names (aerialways) being removed from osm-carto sytle, it’s much easier !
They show up from zoom 15, refresh your cache.
Yves
Il existe plusieurs solutions pour rajouter des chemins dans Openstreetmap.Le dernier-né des éditeurs s’appelle ‘iD’. 
Avant de commencer, peut-être avez-vous une trace.GPX de votre ballade en ski? Sinon, pas de problème: vous pourrez utilisez votre mémoire et une photo aérienne.
Dans tout les cas, connectez-vous ou créez un compte sur www.openstreetmap.org.
Si vous l’avez, prenez le temps d’envoyer votre fichier GPX au serveur à partir du lien ‘Traces GPS’ en haut de la page.
Ensuite, zoomez sur la carte vers l’endroit ou vous allez rajouter votre piste, puis utilisez le menu ‘Modifier’ en haut pour choisir ‘iD’.
Vous voici dans l’éditeur. Lorsque vous serez content de votre travail,utilisez le bouton ‘Sauvegarder’ pour le sauver dans OpenStreetMap.
N’ayez pas peur de faire une erreur :
Si vous avez besoin d’un coup de main, n’hésitez pas à demander de l’aide:
Commençons par afficher une image aérienne ou notre trace GPS. Sélectionner par exemple les couches ‘Openstreetmap GPS traces’ et ‘Bing AerialImagery’.
Pour créer un chemin, rien de plus simple : prenez l’outil ‘ligne’, et repasser sur la trace GPS ou en suivant l’imagerie aérienne.
N’oubliez pas de connecter votre chemin aux chemins déjà existants !
Inutile de faire trop de points, et prenez garde de ne pas suivre toutes les errances de votre GPS : il arrive que celui-ci divague un peu autour de votre position.
Repassage d’une trace GPS
Tracé de mémoire sur l’imagerieaérienne
Cela ne vous semble pas très précis, mais c’est oublier qu’avec le temps d’autres pourront affiner le tracé grâce à leur propre traces gpx, comme ici :
Souvent, une piste emprunte un chemin existant qui est déjà présent. Inutile de repasser dessus.
Lorsque la piste quitte le chemin, cliquez simplement sur le point d’intersection, et choisissez l’outil ‘ciseaux’. 
N’ayez crainte, même coupé en deux le chemin reste connecté. Cela va seulement nous permettre de dire qu’une partie du chemin est aussi une piste de ski de fond, et l’autre seulement un chemin.
Bon, voici notre chemin tracé, mais comment fait-on pour renseigner une piste de ski de fond ?
C’est simple, sélectionner le chemin, et utilisez le bouton ‘Ligne’ en bas du menu à gauche. 
Ceci nous ouvre l’éditeur de tags, que vous pouvez renseigner comme ceci :
Ou comme ça :
Bon, les tags, qui permettent de décrire ce que vous venez de mapper, ça nes’invente pas. Voici ce que vous devez savoir pour une piste de ski :
piste:type = nordic pour le ski de fond
Pour les autres sports d’hiver, il existe aussi :
Plus d’info ici.
piste:difficulty = novice, easy, intermediate,advanced, expert
Attention, ce tag n’est pas là pour renseigner sur la couleur de la piste,mais pour signaler une section plus ou moins ardue. Vous pouvez utiliser cesdéfinitions :
Et voilà ! D’ici demain, vous devriez voir votre piste apparaitre sur la carte OpenSnowMap.org.
Dans un autre post, je vous expliquerais comment renseigner la couleur des pistes et leur nom.
I was requested by a few people to use opensnowmap.org tiles on their website.
Now you can find them on:
To do the same, it’s easy: you just have to tell me so, and use a proper referrer and user-agent. Of course you need to acknowledge OpenStreetMapaccording to this page, and OpenSnowMap.org CC-BY-SA. This is important to tell me before, so that I can check if the server load is ok and warn you about any change.
This only concerns the tiles without hillshading and contour-lines: I’m afraid the load would be to big otherwise.
Of course, if you made any serious revenue thanks to those tiles, maybe you are kind enough to help me and share a part of the Opensnowmap server costs.
The sqlites containing opensnowmap.org tiles up to zoom 16 have been updatedfrom fresh data on 06.03.2014. They can be used on your mobile device orwhatever.
Check here: http://opensnowmap.org/iframes/data.html or directly here http://www.opensnowmap.org/data-download/
Yves
It’s nice to have the largest ski map worldwide at hand with OpenstreetMap. Now with a few mapping efforts, some really useful services could arise from this data. Not only inputting more pistes on the map (there is still plenty to map !) but also in organizing them by ski resorts with site=piste relations.
Now on Opensnowmap, you get some usefull statistics on a particular ski resort.
Some resorts seems to be rather well mapped:
While for others …
There is no ski pistes, just two buildings there.
There is plenty of thing that are not yet mapped in OpenStreetMap. However, I hope these stats will give a good incentive to completely map ski resorts, why not by the operator ?
These stats are obtained by checking the members of site=piste relations.
A few controls have been recently added to complete the piste list view onOpensnowmap.
To obtain the list view, use one of these buttons to
listall pistes in the viewport
select a piste by clicking on the map
search a piste by name
On the list view, you can:
List all pistes of a particular ski resort
View the elevation profile of a piste
Get more info about the resort or piste, including a link to OSM browser
Is there anybody mapping ski pistes any more in the USA? It’s winter there too, but here are the piste edits for last month (red dots) :
Or do I have an issue with my script ?
Anyway, glad to see on the last Modis update that the sun is shinning again above scandinavia: If the satellites can get the snow cover, this means that they can see the ground in daylight.
A few things happened since Christmas. The server had some issues when updating the pistes daily: the (small) disks were full. I took the opportunity to change the server and hosting. All is runnning normally now, and the new server is big enough to handle the relief and contour lines data on the same machine than ski pistes. This means that Opensnowmap now runs with two servers able to serve the same content from two distinct hosting companies. The second one is cheap and slow, but make a descent job as a fallback server.
But that’s behind the scene, what’s really new ? Here it is :
The pistes, Modis 8-days snow-cover, hillshading and contour lines are now rendered as a single layer: 3x less tiles to download for a map view. I am sure your browser will like it.
Piste-only layer is still available for third-party websites (be kind enough to ask me before using tiles).
There is now a feedback on the map when you place the mouse pointer over a piste name in the search-result box.
On the pistes list, a small icon also allows you to get the elevation profile for a single way or single route. This will also show you the route on the map, with an arrow at the beginning to show the followed direction.
Future improvment will be made to improve the interaction between the map and the ski pistes list on the left.
Long time overdue, sleigh pistes are rendered violet with a sleigh icon. Actually this is not clear if piste:type=sleigh means dogs, horses or camels or whatever, so I choose a sleigh as an icon.
Other languages would benefit from your help, too !
After the mobile version were born three month ago, I figured out I could use part of what I learnt to improve the overall look of the main site. I was also suggested some useful improvements from the french mailing-list.
This new skin should also behave better on ie7 (even though a more recent browser is heavily recommended).
The design was sketched with Inkscape before implementation begun, and the complete icon set too: this saved me a lot of time, and the result looks as intended (or even better).
Some tooltips have been added to the menu buttons, so they need your traduction. For the moment, they are in english by default when not translated in the language files (languagefiles).
Let me know your feelings or bug reports in the comments, by email or in github. Yves