I Am Bread is not a misleading title. You play as a piece of bread. More specifically, you only play as a single piece of bread at any given moment --though you can play as many different types throughout the game. What do you do in this game? Whatever bread does when left to its own devices, we suppose!
Want to cling to the walls while slowly driving the owner of your house literally insane? You can do that, just like every loaf of bread I’ve ever owned has done.
Want to race through obstacle courses as a bagel? You can do that too, also presumably like a real bagel would.
Want to play as a horde of crumbs that sneaks into all the places that your owner would think you could never get into? Well, you can’t do that. But you can play as a slice of bread in Zero-Gravity, so there’s that. Boldly going where no slice of bread has gone before. No matter what physics has to say about it.