Each one of those questions leads to a ton of explanations. You need the owners manual for your motor to begin with, and a service manual if you intend to do additional work on it.
If you turned that mixture adjustment, you might turn it back to the original setting. On the chance you turned it clockwise until it hit the stop, turn it c.clockwise half a turn -- might approximate where it was. The toggle switch on the right replaces (presumably) a shut off button. It shorts out the magneto (Unfortunately don't know whether off is up or down -- presumably down I would guess. If you get no spark, try it in the up position. If it's a momentary switch, presumably it's in the run position. The knob on the left is the choke. I can't tell if it's assembled correctly, and you would have to take some of the carb apart to check. Basically, it's in for no choke, pulled out for choke.
The motor takes a 50:1 gas to 2-cycle oil mix. Squeeze the primer bulb in the fuel line and pull out the choke. Set the twist grip as far as it will go c.clockwise with the motor in neutral, and pull on the cord. It appears you have enough water in the barrel -- might keep a hose running into it to make sure.
Edit: well used (might make an offer.):
https://www.ebay.com/itm/1986-JOHNS...896555?hash=item23d3d65d6b:g:nKkAAOSw~O1efOrW
