Shifting my Mongoose mountain bike correctly?

I recently purchased a 21 speed Mongoose mountain bike and I seem to have misplaced the manual. On the right handle bar the shifter goes from 1-7. The other is labled by L-H with several dashes inbetween. What do the dashes mean and how do I used them correctly? Thanks a bunch!

The left side controls your front derailleur that moves the chain between the small,center, and large chainrings in front. Basically so you can achieve gears 1-7, 8-14, or 15-21.

The reality is that on any triple chainring bike (three sprockets in front), you have gear overlap. Gears 5-9 overlap eachother, and gears 12-18 overlap each other. This allows you to shift gears in the rear to find a comfortable point rather than constantly jumping chainrings. You will find yourself using the middle chainring most of the time.

The right shifter controls the rear derailleur and shifts the chain up and down the cogs on the "cassette" (rear wheel gears).

Typically you will only use the granny gear (low on the left shifter) for climbing steep hills. The center is for mild climbs and flats. The high (large chainring) is for flats to downhills.

PS: if your bike doesn't seem like it is shifting properly, either take it into the bike shop for an adjustment or do some reading and do it yourself. See the link below

The L means low and the H means high, this is the gear for the front (the gears on your crank). hope this helps : )