How can I shoot Flames out of my muffler ..?

that depends

you can either buy a flamethrower kit which consists of a spark plug, a remote propane canister, a small power source and a button.
plug goes in your exhaust tip with a line from the propane the power source is attached to the alternator, rev the engine, hit a button, boom flames
OR.......
or you could be running a 500HP race car with straight piped exhaust and have un-burnt fuel run down your red hot exhaust pipe and BOOM flames

i'd go with option B if i were you.....sounds good to me hahahahahaha

it would be my choice