This is a 4 year old mower that is always broken. Right now the mower belt fell off and the
Spindle (not sure what to call the round piece that holds the belt) is loose. When the belt is put on the round piece appears to be crooked. It appears that it simply needs to be tightened down, but turning it just turns the mower blades. Help!

Are you referring to the pulley? If so, it has probably already been ruined and will need replaced. Also check the jack shaft for damage, the jack shaft is the shaft that the pulley mounts on to.