Im not trying to get huge but im kinda skinny with some fatty legs and i would like to get just some muscles in general, if i ride a bike to and from school about 20 minutes each way every week day will that be sufficient?
Only with a lot of hills. Biking is a good exercise for maintenance but of your trying to lose weight your going to need to be rising for hours a day. It is really efficient for traveling.
As with any form of cardio, it depends on how long you do it. You'll burn about the same amount of calories running a mile as biking 5 miles. If you ride any amount of time under an hour you won't see much progress.
biking won't give you big muscles, but it can help. I bike to and from work everyday, around 8km. Llike any exercise it burns calories, so your fatty legs wont gain muscles but they'll be more toned.