These Meat Markers are for keeping track of the level of doneness for a particular piece of meat when you are grilling or barbecuing a group of steaks, burgers, or whatever.
The markers are like little flags. They have a sharp point which allows you to easily stick them into almost any meat. There are flags for five degrees of doneness: Rare, Medium Rare, Medium, Medium Well, and Well Done.
These markers are fun and useful if you are barbecuing for a large group. In reality, I seldom barbecue for large groups so these just sit in a drawer (at least they don't take much space). I also have a 'barbecue branding iron' which serves a similar function and is just as much fun (watch for a future review).
These are 'Single Use' markers. They should be disposed of after use to avoid the transmission of bacteria and other germs.
If you want to accomplish the same thing without buying custom meat markers, you can use toothpicks color coded with Sharpie Markers (only on the end of the toothpick which is not stuck into the meat).
These Meat Markers are somewhat useful, but not really a critical need.