Problem after separating object components... :(

I didn’t even know what title to give to this post! I don’t know what’s going on here.

OK, I separated the end of a cylinder from the main object. (p…) I had the mirror modifier on at the time. In Object mode, I moved the end away from the main cylinder. Both ends moved, because, I guess, the mirror mod is still on in Edit mode. Then I went into Edit mode where I wanted to work on the cylinder some more… but the only things that can even be selected are the separated cylinder-ends! The main cylinder is “locked out” or something!

I’m learning Blender. I think I’m to the point where I can start attempting to actually create something but there’s still so much I don’t know, so I run into problems. Maybe I shouldn’t’ve had the mirror mod on when I separated the end from the cylinder??? Can someone please help?

Separate (P-KEY) creates new objects from the separated parts, so they won’t be able to worked on in Edit Mode at the same time as the original parts that are left over after the separation. In Object Mode, select the Cylinder walls and enter Edit Mode to work on that now-separate object.