As you edit your document you will want to move the caret around so that you can change text in different parts of the document.
Point and click, just as you did when you reopened the document.
Double-click on a word, if you know you want to replace it. The caret will not appear immediately, but the word will be selected and you can overtype it with your replacement.
Use the arrow keys to move the caret one character or line at a time.
Use Page Up to get to the top of the document and Page Down to get to the bottom.