The free video tutorials
in the support section of the site explain the process pretty thoroughly. Also, the manual covers the various types of keying filters if you want more info about each specific one. The basic process is the same though, add the footage to the timeline, apply the keying filter most suitable to the situation at hand ( Auto Difference generally works prety well for greenscreen), and adjust the sliders of that particular filter as required by the footage you are working with.
Also, please don't post in all caps, as it appears that you are shouting.