The fuel used in a nuclear reactor usually comes from?

Mines, usually it is uranium, with only 0.7% (aproximately) U-235 (the isotope that is used for fission), the rest is U-238, known as depleted uranium, or natural uranium. Then it enriched to about 3-5% U-235, unless it is used in a CANDU reactor, in which case it can almost literaly be used straight out of the ground.