I don't know your specific bike, but the general principles apply:

Left shifter = front gears (chainrings) = general gear range (High, Low with 2 chainrings) or (High, Medium, Low with 3)
Right shifter = back gears (cogs) = 'fine tuning' gears within general range

Big chainring, small cog = highest gear
Small chainring, big cog = lowest gear

Experiment with your right shifter, then your left. Once you get the hang of it you'll want to avoid certain inefficient combinations (big chainring, big cog; small chainring, small cog).

Good luck, have fun!