abfahren = to leave (in a vehicle)

anfahren = to start driving / to get into motion after standing still 

jemanden anfahren = to run into somebody (in a vehicle)

verfahren = to proceed in a certain way 

sich verfahren = to lose one's way (in a vehicle)

wegfahren = to drive away from somewhere

These are the most common meanings of these words.  You can find more (often metaphorical) meanings on dict.leo.org.