This article describes the actions of Undo, Redo, and Repeat and gives examples of how they can be used effectively.
Undo is truly a life saver. It protects against word processing disasters, big and small. Don't like what just happened? Press Ctrl-Z and it's as if it never happened. Undo also lets us gracefully change our mind about that formatting change we just made.
Will Undo un-do everything? Not quite, but almost. Very few exceptions exist - one example would be deleting an Excel worksheet - that's permanent the moment it's done. (The solution in that case would be to close the worksheet without saving and then re-open it. If you've been saving changes regularly you won't lose much).
Redo (Ctrl-Y) re-does anything that Undo un-does. Change your mind again about that formatting change that you just undid? Just Redo it.
The combination of Undo and Redo makes experimenting easy. We can switch back and forth between "before" (Undo) and "after" (Redo) as many times as it takes to decide between two formats.
Word's Repeat (F4) feature is highly versatile, easy to use, and can save you a lot of work. Repeat does exactly what its name says - it repeats the most recent action taken, not including selecting text, scrolling, or repositioning the insertion point. It is most often used it to repeat typing or formatting.
To repeat typing, enter text from the keyboard without hitting Enter. Then, move the insertion point to a different location and press F4 to repeat the text. Repeat the text as many times in as many places as you like until you take a new action and that becomes the repeat action.
Repeating text can be even better than using Copy and Paste because there's no need to copy first (Ctrl-C), and it's easier to press F4 than Ctrl-V.
To Repeat formatting, apply the format directly to the first target, and then use F4 to re-apply it to others.
Formatting using Repeat is even more powerful when you use it to re-apply styles.
Check: F4 is especially useful when you need to repeat a command requiring many steps, or one which must access a dialog box buried deep within the user interface.
The mouse and keyboard function as a team when the mouse is used to select a target and F4 is used to Repeat formatting or text.