Disney Infinity is an action-adventure game that relies on players collecting real figurines of popular Disney and Pixar characters. Each time players buy a figurine, they unlock that character and its associated world.
There are two modes of play: Toy Box mode and Play Set Mode. The Play Set mode is a linear campaign, whereas the Toy Box mode is essentially a sandbox where players can build their own worlds. In Toy Box mode, you can play with characters from different worlds (i.e., Disney/Pixar films) but to play co-op in a Play Set you need two characters from that Play Set.