You can type your exact question into Google and find plenty of explanations. Try it! You'll find they're pretty much the same in meaning, except for certain collocations, eg. "start a car" ("begin a car" makes no sense).

Yes, they are basically the same, but they could have slightly different nuances depending upon the sentence. I looked through this site that describes this well (with sample sentences): http://english.stackexchange.com/questions/21043/what-is-the-difference-between-begin-and-start

They basically mean the same, although "begin" has more a feeling that whatever began will last some time.