There are two types of "gangster":
1) A wannabe thug, often illiterate and an inhabitant of a downtrodden ghetto that hangs around in "gangs"; largely associated with the African-American subculture. These try-hard wanna be "gangstas" attempt to make themselves appear like real criminals by graffiting buildings, smoking/selling drugs and trying to looking all "bad-ass and macho an'-shit, yo". An utter degradation of what true gangsters represent (see below), and street wannabe "gangsta"-types don't hold a candle to what real gangsters are.
2) The *real* gangsters are those behind organised crime; most notably the Mafia. Responsible for blackmarket trade, epsionage, organised beatings/assassinations, etc. "The Godfather" portrays the archtype of true gangsters, showing the brutality of mob beatings, shootings, running rackets and abusing woman, alcohol and everything in between. The real gansters are *not* to be confused with the aforementioned definition, commonly used as it might be.
1) I'm da gangsta in da hood, yo. Bustin' shiznitz an' layin' da cuts straight sittin' on yo ass wiv me Colt 40 and homies, cuttin' back a fat split in me crib, yo.
2) "All right, you just shot 'em both. Now what do you do?"
"Sit down and finish my dinner."