Bullets are round or elongated missiles (as of lead) to be fired from a firearm. One example of how to use them is to shoot innocent civilians. The Israelis have also come up with another use: If you have lots of bullets available, you can destroy entire buildings simply chiseling down the walls with bullets until you get to the even more satisfying aforementioned application.
If you search the site for "bullets" you will find them discussed at length. There are several very knowledgeable contributors who participated in those discussions, two of them being nitro and rtharp. If you search using their names you will find the threads also. But to give you a head start, because I asked the same question not very long ago, bullets are a means to "short" a stock at will by avoiding the uptik rule. There are three primary means to do so as discussed on this site. The prop firm method is accomplished by establishing a synthetic short position calls and puts, and being long the stock. This establishes a neutral position. Since you are long the stock, you may sell it without waiting for an uptik, thus exposing the synthetic short. Another method described is accomplished nearly the same way, except only deep in the money puts are used, and long stock. This establishes a near-neutral position, and is executed the same way as above. The third way is to buy the DITM put and long stock, and leg in to the short call position. I don't get this one, but I have a pea brain. All I know is...