The round part you are describing is probably the starter solenoid. I would guess the starter is bad is why you are hearing that click. Get a test light or voltmeter and put it on the starter cable stud at the starter. Hit the start button and see if you have voltage. If so, the solenoid is probably fine and the starter is bad. If you don't have voltage at the starter, follow the starter cable back to the solenoid and see if you have it there. If so, solenoid is good.

Fuel line to carb is large enough it will only fit on one place on the carb. The rest of the smaller lines are vent lines. There is a 1 way check valve that is supposed to be in one of the vent lines, but unless your going deep in water, isnt really necessary. Go to the "engine mounting" parts diagram and it shows what the vent line looks like with the check valve, and tee in it. Looks like this, this is also the rear of the carb looking at it from the bottom(pic robbed from internet) The side you cant see where it plugs in is towards the top right of the carb. Not all of the nipples are brass either, some are black plastic.

 

I don't like plastic nipples.