What steps &what type of paint do you suggest to paint bathroom cabin?

You should use an oil-based enamel and a paintbrush, not a roller nor a spray. Please run a fan in the bathroom until it cures.

Before painting, clean any surfaces and let dry. Lightly sand, fill any holes and wipe down so that new paint will stick.

I have very successfully used TSP cleaner to clean off the dirt and cred, then paint with either a semi-gloss latex enamel using two coats or you can use an oil-based paint. Both of those are good candidates in a damp area.