There isn’t a standard regarding the use of the label ‘sushi-grade fish’. When this label is used in a store, it simply means that the fish is of the highest quality and that you can feel comfortable with eating it raw. Fish are flash-frozen on the boat after they are caught, which kills any parasites that they might contain.
Sushi has a wonderful history and is a very tasty dish that many people enjoy. You can sample the sushi that is offered at your local restaurant, starting with what you are most comfortable with before branching out to try new types. If you are a daring sort, you might also try purchasing high-quality sushi-grade fish, some rice vinegar, rice and seaweed wraps to try to make your own.