Cursor Movement and Editing Keys
Keys that facilitate moving the cursor within forms are both system and keyboard‑dependent. The keys that normally control cursor movement on your keyboard can usually be used to control scrolling and other movements of the cursor in a form.
You can edit text or work in either overstrike or insert mode. In overstrike mode, which is the default, each character you type replaces the existing character beneath it. In insert mode, characters are moved to the right as you enter new characters. The key that controls your editing mode is called the Mode key, and acts as a toggle that enables you to switch modes.