The formatting here is simple enough to understand (I would hope). ^ means ctrl+, so ^x is ctrl+x. M- means meta (generally left-alt or escape)+, so M-x is left-alt+x
It should be noted that this is no where near a full feature-set of either group. This - being a cheat-sheet - is just to point out the most very basic features to get you on the road.
|start a new session||tmux ORtmux new ORtmux new-session||screen|
|re-attach a detached session||tmux attach ORtmux attach-session||screen -r|