Tenderizing is a process to break down the tough muscles or collages in the meat. There are several methods to tenderize meat:
Chemical process - marinading the meat with some acid or powder tenderizers
Mechanical process - you can tenderize a meat by using a tenderizing mallet. You can improvise and pound meat with a variety of heavy objects, including a frying pan. There are also a number of devices that either puncture the meat or make many small cuts as a mechanical way of tenderizing.
Slow cooking: by subjecting meat to a relatively low temperature, e.g. less than 300 degrees, for long periods, collagen will also breakdown.