Oil leaks are not related to head gasket problems. The reason you would need a new headgasket would be because you have a coolant leak that is making it's way into the oil. This would result in a milky looking oil when it is drained. The oil leak could be a fee things. It could be the valve cover, the cam seal, the distributor o-ring, the oil pan, or even you spark plug tube seals. We need to know where the oil is/coming from to tell you what needs replacing.
If you really want to change the headgasket, you need to remove the valve cover, unscrew the head bolts, pull the head off the block. Then take the head in to have it's surface machined so it's flat. Put the new headgasket down, put the head on, and bolt in NEW head studs. Replace the valvecover. All of these things need to be torqued to spec. If you google it I'm sure you will fnd a more detailed instruction. What I said is just the general description of it.