Affordances are the how, signifiers are the what

You can tell that a door’s purpose is to move through it, so a door is an affordance. The signifiers that make a door a door are the doorknob and the clearance around the door because they suggest that the door can be opened or closed. Most signifiers for a door are also affordances. The door handle is an affordance for how to get through the door. The handle is also a signifier because of its long shape, size to fit a hand, and material to stand out from the background. Signifiers are the physical attributes of a component. An affordance suggests how it’s used but doesn’t suggest what it does, like a signifier.