...throughout my document? Like, how do I change ALL of the word that I don't want and replace it with another word in its place.

Say if I used affect when I should have used effect in a 3 000 page document.. how do I fix that without manually correcting it?

Go to Edit>Find and click on the Replace tab. It will all come clear once you're in there.

The "Find and Replace" option in the edit portion of the MS Word toolbar will correct that problem easily.

Click on Find and Replace and follow the basic instructions.l