This might sound rude, but PLEASE don't try this for the first time by yourself. If you have to repeatedly ask "how to do it", you'll probably screw something up. Find someone who knows how to use a proper leak-down tester and have them do it. I really don't want to see a follow-up thread about what damage could be done by sticking the air compressor line in the sparkplug hole and a compression gauge in the other.
Please go get help the first time, watch everything and learn how to do it. If you continue to play with 2-strokes you will eventually need this knowledge and after seeing someone else do it correctly, you'll be good to go.
Dan