Remove chicken from package (or if living in a country where chicken is really fresh, remove feathers, entrails (do not crush any bits) head, feet and wingtips and tail).
In a large bowl or clean sink put the chicken or cut up pieces of meat then pour on cold water until covered then add 1/2 cup of table salt or use less and 1/2 cup of apple cider vinegar.
Move the chicken around gently in this mixture for 10 to 15 minutes. Less time is ok if you see that the skin hangs loose on the meat.
You can add sugar or brown sugar, molasses, honey, karo syrup, pancake syrup or artificial sweetner to the soak, but that and the salt are a matter of taste.
Rinse gently with more clean cold water.
Now you are ready to cook stovetop, oven, crock pot, campfire or whatever.
Even an old elderly bird will usually be tenderized.
My grandma also used this on game to make it tender and moist.
Remember to use a sink cleanser that contains bleach on the sink, because chicken is a funny meat. You need to be careful with utensils after they were touched by any raw meat.
I mention the clean up, because when I was a new cook I did not know.