You might want to start with a basic intro to cnc book. G41 offset compensation is for climb milling, G42 is for conventional milling. Left and right simply confuse the issue. A good book or manual with illustrations and accompanying sample code will be the easiest. As they say, a picture is worth a thousand words.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.