You have two choices. You can buy coffee grounds from the stores, or buy beans and then grind them. If you buy them from the store, you save yourself a lot of hassle and effort. However, as soon as your beans have been ground the oils and flavors will start to degrade, compromising on the taste. For a few minutes of work, I think it’s worth investing in a grinder. It can be a small manual one, or a more substantial one, and you don’t have to spend hundreds of dollars either.