This might help:
http://www.eatsushi.com/
I know I'm not going to do it justice, but the short version is that sushi involves seafood and/or vegetables, rice, and (in the case of rolls) seaweed. Tuna, salmon, and yellowtail are quite common and are used raw; shrimp and eel are also used, and are cooked. You can also make vegetarian sushi with carrots, cucumber, avocado, etc. You dip a piece of sushi in soy sauce then eat it.
Because the fish is raw, you have to be sure it's absolutely fresh and carefully handled.
Professional sushi chefs take their trade very seriously and must do long apprenticeships before going out on their own.
ohhh, now I want sushi
