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.
When someone shows you who they are, believe them.