The first thing you need to do is decide whether you want to do a fish in or a fish less cycle. Obviously a fish in means the fish will be in the tank while it is cycling and a fish less means you will first cycle the tank then add the fish.
The basic run down of a cycle is you introduce an ammonia source to the tank (in the form of: pure ammonia, fish food, fish waste) then a bacteria forms which absorbs the ammonia and produces Nitrites. After that a second bacteria forms which absorbs the nitrites and produces nitrates. You will know when you are cycled because you will have readings of 0ppm Ammonia, 0ppm Nitrite, and 5-20ppm Nitrate constantly for several days straight.
Here is a link about fish in cycling. It is MUCH harder than fish less but I prefer this method because it is more natural IMO.