How do I tighten the auger belt on a toro 521 snowblower

What model 521 do you have.
I thought the augers on those drove off the disk plate same as the traction .check out the disk and drive pulley
If you check on the cable there might be a adjusting nut that will tighten tension thers about three different models of 521,
Luck

The toro 521 is model 38052. Everything turns fine and fast but even a small amount of snow stops it up and it gets clogged. I do not know what to do.

Check on the auger see if you can spin it with the motor off if so it should be real hard , they have shear bolts that go through them could be one of those are broke.
Other wise make sure the engines running fast enough at high rpms
Luck