I have decided to jump into the world of biking and recently purchased a mountain bike. My only biking experience was as a child on a ten speed my father put together for me. I am ashamed to say that I haven't ridden in many many years...and well, this concept of shifting gears is completely foreign to me. So far I have only ridden on a fairly flat bike path but would like to venture out onto so more challenging trails. I have two sets of gears-- one at levels 1 2 3 (3 being the highest) and 7 sub levels within each of those gears. Oh my, had no idea there was so much to biking now. Can someone take pity on me and explain the concept of shifting gears? When should I have it on the higher resistence, when should I shift down etc? Thanks!