Inside corners get folded Paper tape only. Even at the ceiling.
Some guys might use a flex bead on Off Angles to help straighten the line, but paper tape also works there as well.

 

Paper tape has a fold line for that.
You can get a trowel for the inside corners that are get for us amateurs I use the cheap plastic one for the taping and bigger metal one for the next coat and then go the 8 or 10 blade for the finish, if that gives you trouble do one side and let it dry before doing the other side. And then a little more to fix that mess.

 

I painted a house once where the idiot hanger put corner bead up on the inside corners - the finisher was not happy! Once you get the hang of it, paper tape works great on the inside corners. Corner bead is only for outside corners!

 

Trim Tex for one makes an inside corner bead and if your corners are rough it's great. Also Home Depot sells a product called StraightFlex perfect 90 that is a vinyl corner tape and for someone not used to paper tape. And for some of us that are but want something easier It costs more but is well worth it. You can also get paper tape that has a metal corner bead behind it. Home Depot also has it back in the area where the mud is it comes rolled up in a box as does the straight flex.

Oh and the straight flex is tapered so the edge is almost flat. This makes it easy to blend in where it meets the drywall.