I'm also a beginner and I'm curious too.
I just finished a batch today and after moving the fermenter to my refrigerator, all of the yeast had sank to the bottom and mixed in with the trub. (I had a lot of trub because it's a 1 gal batch and I can't afford to waste that much of it.)
After some research, I decided to swirl it around and get it back into suspension. This seems to have worked because the trub sank to the bottom and it looks like the yeast was still floating around. I had a blowoff assembly hooked up the whole time so there's no way any extra oxygen got in.
So it seems that the general concern is not adding any oxygen after pitching the yeast. But, as long as the fermenter is sealed, it should be ok right? It did start bubbling after I swirled it but it could have been a coincidence.