There are three main ways to tenderize your meat: mechanically, chemically and time with moisture.
Mechanically tenderizing is when you cut, pound or grind the meat. This breaks down the elastin in the meat; examples include hamburger, cubed steak, pounding with a meat mallet, and slicing across the grain (this one shortens the elastin).
Chemical tenderizing is when you add an enzyme substance (liquid, powder, etc.) that break down the elastin. Some of these enzymes include; marinades, and commercial tenderizing products containing papaya and pineapple.
The last tenderizing technique is when you cook the meat at a relatively low temperature for a long period of time with moisture. This one is probably the most common and includes: braising, simmering or poaching.
You can use a combination of two or all three if the meat is fairly tough.