The OBS softkey is enabled when a flight plan is active. If you turn OBS on, the next waypoint is treated like a VOR, and the CDI course pointer sets the course to that waypoint. One handy trick is to switch the autopilot to heading mode, when the airport is the next waypoint, then press OBS and rotate the CDI knob to the runway heading. Then you've got an extended centreline to aim at for your base join. OBS works as you'd expect with VORs.
The SUSP key is used in conjunction with instrument landings. It is shown at the missed approach point. Press it after you've executed the missed approach instructions, to receive guidance to the next waypoint.
I've found Max Trescott's
G1000 Glass Cockpit Handbook to be very useful - perhaps because it's not free!
