track to Tibet, western Himalay

Your question is not really suited for this help site (too special/specific). However, since are are here already...

Are you searching for routing based on OSM data? There are many routing engines and instances. See Routing in our wiki. Eg. part 1 and part 2. Note that those are not recommended hiking routes or whatever. Those are just fastest connections based on the existing data.

For easy tour planning I recommend http://www.gpsies.com (track creator does not need a login). Also see this list. At gpsies (and the many similar websites) you also find suggested tours from other users. If you are lucky there may be a suggested tour.

You can find much more general answers on this site here. Click the tags below your question.

This is a very basic question, anyway I will try to give you a short answer:

Please look at the desired region using www.openstreetmap.org and checkout if a track/road/... already exists. If the area appear to be mapped already, you might try a routing service with global coverage and your desired routing profile to calculate a way trough this region.
If there are no streets mapped in that region it might be possible that this is the real situation or that noone mapped there before. In last case, we would appreciate any contribution back to OSM :)

Be warned, I would never rely only on one source of information if I would plan a long trip in a unknown country. So better get feedback by local guides/books/...