When selecting a hero, there is an exclamation mark inside a circle just below their name (top-right corner). What does it mean? What happens if you press it?
This button will give you an overview of that hero's abilities, what they do, and what buttons they are bound to. This is what it looks like for D.Va:
As you can see, the screen shows you D.Va's role, her two ultimate abilities, her three normal abilities, and her passive, as well as a general indication of how difficult she is to play on a scale from 1 to 3 stars, with 3 being the hardest.