Tsumami means you are eating without rice, that is, sashimi. For sashimi, you get a mound of wasabi, some greens similar to watercress, and maybe wakame seaweed, instead of the ginger. You can still change your mind and have both sushi and sashimi. In the U.S. you usually get wasabi and gari, and that's that. The gari is a palate cleanser, nibbled between pieces of sushi.
Some people devour it, others barely touch it.
There will be a small empty sauce dish in front of you, into which you pour a small amount of soy sauce for dipping your sushi. A soy sauce bottle or pitcher will be nearby. For sashimi, mix some of the wasabi paste into the soy sauce dish, to taste. The right sauce for the right dish. Eel sushi is spread with its own dark sauce, and should not be dipped in the soy sauce.