learning how to ride a mountain bike

Question
i just bought a mountain bike and have no clue what i am doing.  i bought the fuji nevada 2.0, on the right hand side it has the gears and on the left handle bar it has some other dial with a 1 and a 2.  every time i put it in the 2 spot the chain clashes against the chain guard thing.  also every time i put the bike in 8th gear on the 1 setting it does the same thing.  i have only really been riding on flats and small inclines cause i don't know what i am doing, i find myself spinning my wheels alot.  do you have any advice for me.

Answer
Ricky, I have discovered your question in a pooled file. I hope you have had some good luck with your riding.
The gear on the front of the chain, on the crank, is the sprocket and on the back wheel, the cassette. You have discovered the left grip controls the sprocket, the cassette by the right hand.
Many mountain bikes have a triple sprocket crank with a 7 or 8 geared cassette. Apparently yours has a double sprocket.
Try this for an illustration. Get two pencils, table knives or anything about that length and straight. Lay them out one behind the other about 2 feet apart, bicycle chain length. Now get a string, the belt holding up your pants or anything you prefer and use it to "connect" your "pencil sprocket" and your "pencil cassette". That is the way your chain runs. Now move the sprocket pencil 1/2" to the left and move the cassette pencil 2" to the right. This is the chain configuration in your "1-8". The chain rolls straight on the sprocket, bends to the right, moves across at a sharp angle bends to the left, and then rolls straight on the cassette. Chains are made to bend up and down, not side to side. ALL bicycles make a lot of noise in a gear that requires the chain to be a both extremes. Running in either high or low gear shifting back and forth on the middle 4 or 5 cassette gears will result in quite running. The noise, by the way, is only an irritant, there is nothing wrong with the derailuers. Running continually like that will cause premature wear on the chain, sprocket and cassette.
If your wheels are spinning you are losing traction and you need to either get off the saddle and shift your weight over the rear wheel or up shift to a higher gear development, larger sprocket or smaller cassette.
Get your bicycle off the ground by hanging the saddle over a piece of pipe or tree limb. Turn the crank by hand and use the other hand to shift through the gears. You will see the chain running angle I referred to and if you turn the crank and constant speed you will see the gearing.