I read that the flash that comes with the camera acts as a wireless trigger for off camera flash?
Yes. It can be used as a master in the four-thirds "RC" smart optical (wireless TTL) scheme.
If so what flashes can I use to work with them?
Anything that can be an RC slave, so Olympus and Panasonic flashes for sure (e.g., an FL600-R/FL360-L). 3rd-party makers like Nissin and Metz also make RC slave capable flashes. But not Godox or Yongnuo.
for instance can I use Yongnuo yn560iii ...?
Weeeeellll. Not as an RC slave. So, no TTL/HSS/power commanding over optical.
But the YN-560III does have S1/S2 "dumb" slave modes, which use a sensor to fire the flash in sync with the shutter. They will respond to ANY flash burst, so if the Oly flash is just being used on-camera as a flash (not a wireless master), and in M mode, S1 fires in sync, and in TTL, S2 fires in sync (skips the metering "pre-burst").
The YN-560II's built-in radio receiver is for the Yongnuo RF-602/603/603ii/605 and YN-560-TX triggers. And only the YN-560-TX can remotely control the YN-560III's power level.
Also. Today? A Godox TT600 + X1T transmitter is probably a better bet for the same price as a YN-560III + YN-560-TX, because
Godox's X triggering system can actually give you TTL/HSS with Oly gear if you decide you want to add it (which Yongnuo's stuff doesn't), and even though the TT600 is manual-only (like the YN-560III) and doesn't do TTL, with the X1T, you can still get HSS over radio (unlike the YN-560 combo).
... and will it also trigger studio strobes like Paul C Buff?
The Buff lights all have a "dumb" optical slave sensor, like S1 mode, so again, if you just use the Oly flash as a flash, not a wireless commander, and keep it in M mode, you can trip the lights remotely. The only way to get remote power control over Buff lights, though, is to use their CyberCommander or CyberSense triggers. And there's no way to use either with a speedlight.
Again, Godox might be better if you plan on having control over both speedlights and studio strobes.