You can toggle between these two modes by pressing a key; if you don't think you'll ever use the over type mode, you can also permanently switch it off in Microsoft Word. Press the "Ins" key to toggle over type mode off. Depending on your keyboard model, this key may also be labeled "Insert."
If you have a small child, you will know how they can somehow change the settings on you pc, tablet and phone. My little one makes us laugh every time she changes some setting on the TV that we did not even know existed.
The other day she almost order something from ebay.
But my laptop keyboard is her favorite. She loves sitting with me and "work". So when she some how changed all the settings on my keyboard it took me a while to figure out some things. One being how to stop deleting as you type when trying to correct or change your spelling.
I tried the above by selecting the "ins" on the top roll of my keyboard but nothing happened. After some very annoying typing and re-typing, I noticed that my keyboard also have "ins" under the zero key of the number keypad. And it work!!
Problem solved and you do learn something new everyday. :-)