Swing the cat in

[upreal]

I have read a novel and found idioms such as swing the cat in and hands folded on his desk. what do the idioms mean?

[JMurray]

not a teacher

The phrase "not enough room to swing a cat", means the space/room is small and usually awkwardly so.
It's often thought to refer to the "cat o' nine tails", slang for a type of whip once used in the navy. However there is some doubt about this origin.

No room to swing a cat

"Hands folded on his desk" is simply descriptive, it's not an idiom.
A photo of hands folded on a desk.