if your asking about halo3 you could play the campaign thru for fun, but if not then i suggest getting a good group of people from HFF and sending them all FR and start playing customs DONT TOUCH MATCHMAKING!!! You will be very unskilled @ first and have trouble navigating maps and if u play matchmaking (although you might have fun @ first) eventually you will become rank locked and no matter how bad you pwn people on your level, you wont rank up. Also in my opinion customs are alot more fun, but you can do MM if you want.
send me a FR i will help u out my GT is golfball is bak my other GT is na golfball