If you don't know how to butterfly a chicken you should definitely learn how (see the video How to Butterfly a Chicken
to find out how). It's a little tricky the first time, but once you get the hang of it, it should go by quickly. To butterfly a chicken, place the chicken on a large cutting board breast side down. You will need a knife and a pair of kitchen shears. Turn the chicken so that the tail is towards you and with the kitchen shears begin cutting just to the side of the backbone. It takes a bit of a grip to get through the bones, but it shouldn't be too difficult. Cut all along the side of the backbone to the neck of the bird. Now you can open it up. Cut along the other side of the backbone and completely remove it. Open up the chicken and flip it over so that it is laid out on your cutting board. Press down on the breast until the chicken is flattened. You might need to trim up the rough edges a little.
There are a couple of variations you could try in this process if you really don't want to butterfly your chicken. I'm demonstrating the traditional method but you could keep your chicken whole and either do it as a Rotisserie Chicken or as a Beer Can Chicken.