So the one by the crank handle adjusts how much force it lets the weight of the bait put on the spool to pull at the spool.

They should be used togather.... I hate when people say on just use the tension knob to take out the side to side movement lol

Most of these answers are just where did they come from?

Tie on the lure you are going to throw. Hold your rod at a 45 degree angle with your lure dangling about a foot below the rod tip. The spool tension knob will be on the side of your reel along with the cranking handle. Push the thumb bar. This knob will control how fast the lure falls. If it doesn't fall, loosen the knob. If it falls too fast, tighten up the knob. The lure should fall and when it hits the floor, your spool should not backlash. After your have the tension knob adjusted properly, set the centrifugal (or magnetic) "brakes" as high as possible. Start making practice casts. At first, you will not be able to cast very far. Lessen the brake adjustment one setting a time and make more practice casts. Eventually you will begin to get minor back lashes. At that point, increase the adjustment one click back on the brake.

The more time you spend fishing with a bait caster, the better you will get at it. But remember, no bait caster is "backlash proof."