Sushi is made with vinegared rice, sugar and salt. It usually has a filling or decoration featuring fish, algae, vegetables or eggs.
These items can be raw, cooked or marinated and served in a bowl of rice, rolled up in algae or rice or even used as a filling for a tofu pouch.
Sushi is different from sashimi, which mainly consists of fresh fish, meat or mollusks cut into thin slices and served along with a sauce (soy sauce, wasabi or ponzu sauce, for example) and a simple garnish (like daikon root cut into strips).

Futomaki (large roll).
This is a large, cylindrical piece with nori on the outside. It is usually two or three centimeters in diameter and four or five centimeters long. They are often made with two or three fillings that are chosen for their complementary tastes and colors. Typically there's only one type of filling for the simple reason that more can't fit.