[eeyore]

i'd tend to suggest sticking to auto until you have got your composition etc down then when you want to take more creative control use either aperture priority (AV) - where you select the aperture and the camera selects a speed to match , or shutter priority (TV) where you select the speed and the camera the aperture. Ocassionally you may wish to use Manual (M) where you select both but this can be slow to set up if you are shooting action.

by the way i have an advice sheet for beginer wildlife photographers, which covers all this in more detail, that i'd be happy to send you if you pm me with your email address