The fitting under the engine is the crankcase vent. Put a piece of tubing on it long enough to have it hang out the bottom of the cowl. This has to be vented to the atmosphere.

The one on the needle valve is the fuel inlet for the carb.
The one on the exhaust pipe goes to the fuel tank vent line

The one on the side of the air intake is used to prime the engine. You don't really need to use this. Just put your finger over the exhaust pipe with the tank vent line on it and flip it over a half dozen times to prime it.