How do gears work?
The right hand shift levers work the rear derailleur and the left hand shift levers work the front derailleur. The higher the gears the easier it is to pedal.
High gears are suitable when climbing up a hill whereas small gears help gather faster speed but take greater effort. So if you're riding along in gear number 3 for example and are coming to a stop sign, gradually switch to number 5 or 6 so it's easier to pedal when you start up again. Or if you're coming to an incline or a hill, do the same thing so you don't have to work as hard.