[A start? A start on what? Well, too late to back out from explaining now. She launches into lecture mode:]

Psi is the power of your mind, acting on the world. Anybody is capable of using psi, but normally your brain prevents it, because using it can overtax your brain. However, under certain circumstances, one can lift that limiter and let all of your brain cells fire simultaneously. Nine o'clock, one robot, fifty meters.

If you can do that, you can use psi. Psi powers break down into three types. There's Burst powers, which have affect your physical surroundings. Things like telekinesis, pyrokinesis, and the like are Burst powers. There are also Trance powers, which affect people's minds and move information. And, finally, there are Rise powers, which improve one's own body, senses, and healing.