Operation Panel
The panel for adjusting the settings of the operation you just performed.
After running any operator in Blender (a move, a bevel, adding a cube), the operation panel appears in the bottom-left of the viewport, letting you adjust that operation's settings after the fact. The shortcut to bring up the most recent operation is F9. Learning to lean on it turns rough actions into precise ones.
Related: Modeling · Move, Rotate, Scale
These fundamentals are covered hands-on in Blender Geometry Essentials 01, free with a free account.