Components are Principle's version of a symbol. A component can be in multiple locations and artboards, and a change to it will affect all instances. A component can also contain artboards itself, and interactions within those artboards. Using components, you can build rich micro-interactions into your prototypes and test small delights. One current limitation is that you can't overlap gestures.. meaning you can't assign a tap micro-animation with a tap gesture to another screen. You could however, use a component with no tap gesture, which is what we'll do for the menu button. For something such as a "Like" button, you could build all possible states of that component and basically bake your micro-interaction into the containing artboard, no transitions needed.