There are some types of sushi. Nigiri-zushi are hand-pressed mounds of rice with a dab of wasabi and a piece of various ingredients on top. Popular nigiri-zushi are maguro (tuna), toro (belly of tuna), hamachi (yellowtail), ebi (shrimp), and so on. Maki-zushi are sushi rolls wrapped by nori seaweed, such as tekkamaki (tuna rolls), kappamaki (cucumber rolls), and more. These are also called norimaki. Inari-zushi are deep-fried tofu pouches stuffed with sushi rice. They are brown and oval-shaped. Chirashi-zushi are sushi served on a plate/bowl with different ingredients on top of rice.
Important seasonings are soy sauce and wasabi (Japanese horseradish). Soy sauce is used as dipping sauce. Wasabi is put in nigiri-zushi or is mixed with soy sauce for dipping. Also, pickled ginger called gari is commonly served with sushi. Green tea (it's called agari in sushi restaurants) is the best drink with sushi.
In traditional sushi restaurants in Japan, sushi can be expensive, depending on what you eat. You can usually order a set of sushi with a fixed price or order your favorite sushi pieces as you eat. For reasonably priced sushi, there are places called kaiten-zushi, where the sushi plates circle around the eating area on a conveyor belt. There are kaiten-zushi restaurants everywhere in Japan. When you go to a kaiten-zushi restaurant, you wait until your favorite sushi comes near you, then pick up the plate from the moving table. If your favorites aren't available on the moving table, you can also order them. Prices vary but usually between 100 yen - 300 yen per plate.