>>1347891>how does one find these MTB trails?There are websites that have directories of mountain bike trails. Just do a web search for mountain bike trails in your area. Some trails are at ski resorts and are maintained by the ski resort staff, whereas other trails that are more in wilderness areas are built and maintained by mountain bikers.
>Do you ride to the topDepends. Most people cage to the trails unless they live really close, then they might ride from home. There's usually parking lots by the trails. It's kind of like going hiking. You cage to the trailhead parking lot, then head out on the trail. And yes you ride up and down. Some trails are steep, some are flat. This kind of riding is called 'cross country' or 'trail'.
The other kind of riding is 'downhill.' Specifically, lift-accessed downhill or shuttle-accessed downhill. Lift-accessed downhill takes place at downhill ski resorts during summer. People take the ski chairlifts up (there will be a hook on the chairlift for the bike to hang on) then ride down. For downhill that doesn't take place at ski resorts, there are trails that run alongside/near roads. People will take turns caging up with their friends, one will drive the car down and the others will bike down the trail, and they'll take turns being the downhill cager. Also, some popular places have shuttle services that work the same way except it's a paid driver instead of a friend.
On some trails, some people choose to bike up and down the trail while other people do the shuttle method at the same trail. Of course, with a lot of trails, the shuttle option is not an option because there's no road anywhere near the top of the trail, or because the trail has lots of ups and downs. In these cases you have to just ride the whole thing.
Droppers are because people often prefer to have a higher seatpost on flats and climbs, and lower on the descents (you'll be standing a lot during the descent, sitting a lot when climbing and on flats).