A foam roll is typically an 18” long, 6” diameter cylinder made out of dense foam. It generally costs less than $20. To use it, you lie on top of it, using your body weight to press the roll in to the targeted area. You move yourself over the roll, working the targeted area back and forth across the roll.
You can apply the foam roll to a number of areas, some of the most popular are the hamstrings, the IT band, quads, calves, glutes, and back. The level of intensity is up to you. For example, you can give yourself a mild massage by placing both hamstrings across the roll or a more intense massage by concentrating your body weight on only one hamstring. As with most good massages, it may hurt a little bit until you loosen up. Be careful!
The foam roll is great for loosening up stiff muscles and recovering from minor muscular injuries. I once pulled a hamstring running uphill on loose gravel and had to walk home with a knot the size of my fist in my left leg. A single session with the foam roll worked it out and got me back to pain-free running. I use the foam roll once or twice a week, depending on how hard I am running and how sore I am.
There are several versions of The Stick, with different lengths and different degrees of flexibility. You should find a store that carries The Stick and try it out before you buy, to make sure that it is the right one for you.
I have the 24” Original Stick, with the blue handles. This runs about $42. It has medium flexibility. I find that it is better than the foam roll for getting at smaller muscle groups, concentrating on the quad muscle on the inside of the thigh (vastus medialis), for example. It also requires more strength to apply it, since you are not relying on your own body weight to provide the pressure. I use The Stick occasionally, when the foam roll can’t get to a particular target area.