The "insert" feature in Microsoft Word allows you to go back in a sentence or paragraph and insert more type or characters. By default, this feature is usually turned on. When it is on, you'll see the letters "OVR" grayed out at the bottom of your Word document (in the beige status bars).
The "overwrite" feature in Word does the exact opposite of "insert". When "overwrite" is enabled, you can still go back and edit text, however instead of inserting text, you'll now overwrite existing text (i.e., replace existing text with new text). When the "overwrite" feature is turned on (which means "insert" is turned off), the characters OVR in the status bar will be black.
Most folks like the "overwrite" feature to be turned off so that they can go back and insert text later. But sometimes, it gets turned on by accident and they don't realize it until they try and go back and edit text.
So the next time you're typing along and notice that you're overwriting text as opposed to inserting text, glance down at the status bar and check the characters OVR to see if it's grayed out or black. If it's grayed out, you know that the "insert" feature is turned on. And if it's black, then you know the "overwrite" feature is turned on.
You can easily turn these features on and off by hitting the "insert" key on your keyboard. Go ahead and test this. Open a word document and check the status OVR. Then hit the "insert" key on your keyboard and watch it change. Then hit the "insert" key again on your keyboard and watch it change again.
When you're through testing this feature, it's best to leave "overwrite" off (which means OVR will be grayed out).
That's all there is to turning this feature on and off.