air/fuel ratio can be somewhat measured by the way your spark plug looks after a little bit of use. It helps in tuning your motor and keeping it from running lean will keep it from over heating and melting down. your plug should be anywhere from brown to an ashey grey type color. you may want to search the net for pictures of how a good running engines plug will look, as its hard to describe.
the float bowl is the bowl shaped thing at the bottom of your carb, just make sure you keep your carb as level as possible, no need to break out real level you can eyeball it and be just fine, whatever you do, don't mount it like your engine.