What makes an engine misfire?

A misfire is also called "predetonation". Usually it is caused by spark plugs or some deposit in the cylinder / head that is not transferring heat to the cooling jacket, and is prematurely igniting the fuel. Other options might be bad timing, shorted spark plug wires, or carbon tracking under the distributor cap.

could be alot of things, but most common would be spark jump from a bad wire. look inside your engine compartment at night and see if you can see spark from a wire arcing over to the block or something else that's nearby. look on both sides and move your plug wires around. also pull all wires 1 AT A TIME and see if it makes the vehicle idle worse. keep pulling and putting back on each wire till you think you found the bad wire. the bad wire will be the one that when you pull it- THE VEHICLE RUNS THE SAME

or you could have a bad plug, which will be similar to solving as the wire pulling technique.

or you could have something bad inside your distributor weather its points or HEI type distributor.

or it could be timing problems besides that. in which case most carport mechanics need professional assistance.