Bounce Selection and Render in Place both create new audio files.
You can use Bounce Selection to combine separate audio events into a single event and audio file, or you can use it to just grab a certain portion of an audio event and make a new file/event out of that section. You generally use it when you’re just consolidating or isolating a bit of audio for use inside your project. (I always use Bounce Selection after comping vocals.)
Render In Place can work on audio or midi parts. It can work on ranges, events, or whole tracks. The main purpose is to render out stems for export into other tools, but I’ve used it before as a sort of “permanent freeze” when I’m nearing completion of a project.
Bounce Selection can’t do everything Render In Place can do, but it’s quicker to use if you’re simply planning to consolidate a few selected audio events inside your project.