Westerners will be more familiar with sushi being a seaweed (Nori) wrapped rice filled with seafood or vegetable filling. But sushi is much  more, sushi refers to a broad range of food prepared with sumeshi or sushi meshi which is vinegared rice. 

It is made from vinegared rice combined with a topping or filling of fish, seafood, meats, vegetables, or egg. The topping may be raw, cooked, or marinated; and may be served scattered in a bowl of rice, rolled in nori, laid onto hand-formed clumps of rice, or stuffed in a small fried tofu pouch. Vinegared rice is really the only common ingredient between the types of sushi. 

Some of the more popular Japanese Sushi include-

Nigiri-zushi (hand-formed sushi). Is one of the most typical form of sushi. Nigiri-zushi is an oblong mound of sushi rice which is pressed between the palms of the hands, with a speck of wasabi and a thin slice of a topping, sometimes it is tied up with a thin band of nori .

Makizushi (rolled sushi) this is the what most western people are used to. It is a long tube like rice and filling roll with a nori outer. The filling can contain just about everything, although avocado is not a usual ingredient like it is in the west. 

Temaki (hand rolls) Temaki are  large cone-shaped piece, with the nori on the outside and the ingredients spilling out the wide end. A typical temaki is about ten centimetres long, and is eaten with the fingers since it is too awkward to pick up with chopsticks. 

Uramaki (inside-out rolls).. A medium-sized cylindrical piece, with two or more fillings. Uramaki  The filling is in the center surrounded by a liner of nori, then a layer of rice, and an outer coating of some other ingredient such as roe or toasted sesame seeds. 

Oshizushi (pressed sushi). This is a rice block that is formed using a wooden mould which is called an oshibako. The chef lines the bottom of the oshibako with the topping, covers it with sushi rice, and presses the lid of the mould down to create a compact, rectilinear block. The block is removed from the mould and cut into bite-sized pieces. 

One of the more popular types of restaurants servingsushi is the sushi train restaurant. Here prepared sushi move around on a conveyor belt past the diners seat. The customers choose the sushi they want as it passes and then at the end of the night they are charged for what they take based on different prices for different coloured plates. Its a great way to experiment and fun.