What is an oven anti-tip device and how do you install one?
It's a bracket, with a U-shaped slot. Depending on the model, it is screwed either to the floor, or to both the floor and the wall behind the oven.

 


You slide the oven's rear foot underneath the bracket, and it holds the oven in place in case you step on the door while it's open, preventing your pot of boiling water from sliding off the top onto you.

Installation is usually just a matter of:


Sliding the oven out;
Cleaning all the gunk that's collected there over the years;
Measuring where the foot will be when the oven is back in its spot;
Screwing the bracket into the floor, and the back wall if it's an L-shaped bracket.
Sliding the oven back in, making sure the foot goes under the bracket.