If you come to Japan, you must eat real Sushi.
Sushi (すし, 寿司) is a Japanese food consisting of cooked vinegared rice sushi-meshi (鮨飯, "sushi rice") combined with other ingredients (neta [寿司ネタ]), usually raw fish or other seafood. Neta and forms of sushi presentation vary widely, but the ingredient which all sushi have in common is vinegared rice. The rice is also referred to as (shari [しゃり]) and "sumeshi" (酢飯, "vinegared rice").
by Wikipedia
You know, Sushi is a very traditional dish in Japan. So there are many rules behind.
Oh, you don't know them?
Don't worry.
If you watch this video, you understand how to order Sushi in traditional Sushi restaurant.

Hehe, I hope you understand Sushi traditions.
Please visit Japan and eat the real Sushi.