CE is Clear Entry. If you want to hit 2 x 4, but accidentally press 2 x 44, you can press the CE button before pressing = to clear the 44 but not the "2 x" part.
C will clear all of it so you can start over at the beginning.
Pressing CE twice may or may not clear entries in reverse order, depending on you calculator model.
I am using and loving Solve by Pomegranate Apps. Multiple workspaces and advanced functions available a swipe away. It doesn't seem to be available anymore, and it looked like the company was hitting hard times when they dumped things like Trump quotes and other shit apps into the store. So, apprehensive to recommend because of weirdness but best calculator ever.
Edit: down arrows barely meant anything on Reddit and they mean literally nothing here. Fuck you and your annoying orange. Peace out, hugs and kisses.