Most of the time it's like a screw or a nail piercing the tire. That can be easily fixed for cheap at a local garage.

If you're broke and can't afford new tires, be careful if you buy used ones.

I bought a used set of summer tires and they were being kept under a backyard balcony and had been there for several years. The rubber turned to plastic. Even though the tires had no wear on them, I couldn't used them because they hadn't been stored properly.