AAVE is a form of American English spoken primarily by African Americans. Although an AAVE speaker's dialect may exhibit regional variation, there are still many salient features. The speaker's ideolect could contain all or only a few of these features.
There are two main hypotheses about the origin of AAVE. One is the dialect hypothesis and the other is the creole hypothesis. The dialect hypothesis is the belief that African slaves, upon arriving in the United States, picked up English very slowly and learned it incorrectly, and that these mistakes have been passed down through generations. In other words, AAVE is just "bad English." The creole hypothesis, however, maintains that modern AAVE is the result of a creole derived from English and various West African Languages. Slaves, who spoke many different West African languages, were often thrown together during their passage to the New World. To be able to communicate in some fashion they developed a pidgin by applying English and some West African vocabulary to the familiar grammar rules of their native tongue. This pidgin was passed on to future generations, and as soon as it became the primary language of it's speakers it is classified as a creole. Over the years AAVE has gone through the process of decreolization and is beginning to sound more like Standard English.
Absolutely nothing. The biggest problem that AAVE speakers face is prejudice. Most people believe that AAVE is sub-standard to SE for some reason. AAVE is just as legitimate as American English.