How to flatten chicken breasts? Link to a video demo by Amanda or Merrill?

I smack them between two sheets of plastic wrap with the bottom of a Granite Mortar of a mortar and pestle set.

A tab for videos on the site would be nice.

Google is your friend! It's really not that big or deal... Slice breast in half cover with plastic wrap
and whomp 'em till they are the thickness you want. Viola!

I spent a good amount of time looking for a vido demo on pounding a chicken breast on this site, but could not find one. What is it you need to know? Here are a few pointers:

1) use plastic wrap or a plastic bag. This ensures that you don't make a mess and it also contains the chicken juice which limits cross contamination. This also helps you not destroy your chicken breast. I prefere to use an open ended (non re-sealable) plastic bag. These are easier to deal with in my opinion as plastic wrap tends to stick all over the place and it doesn't completely seal the chicken juices. You can get a box of these at any grocery store in the ziplock bag section.

2) use a meat tenderizer. The goal is to make the chicken breast an even thickness all around so that it cooks evenly. Place your chicken breast inside the bag or between two sheets of plastic wrap. Start at the thickest part and lightly pound, working out wards. You don't need to use a lot of force, just use your best judgement.

That's pretty much it! There are multiple videos on Youtube which you can search for. I recommend doing a quick search if you feel you need a visual demonstration.