Legit playing (or legit hacking) is when you use an engine in an advisory role only i.e. to give you suggestions.
To legit play using GM Cheems, go to
Gameplay > Run Analysis For and choose who you want the engine to create suggestions for.
You can also configure the engine to compute up to 5 different lines, in
Gameplay > Number of lines
Each line will be shown in the sidebar, along with its score in centipawns.
When you hover over each move in the line, a preview of the chess board will pop up, so you can easily see how the moves play out.