Automatic Transmission Question

Hey I just got my sisters 89' Probe LS. It's an automatic but it has a different transmission. It's called a power boost transmission and it has a little button next to the shifter. If anyone could explain what this actually does could you tell me. Also there is a button on the shifter itself that says manual underneath the regular button. Could someone explain what this does, since the car has only Low, Drive, and Overdrive? thanks