Why are F-22 Raptors a stealth aircraft?

The F-22 uses a few systems, and lessons learned from the F-111 to be a Low observable aircraft.

The engines emit a heat signature that is unmistakable, but they have used heat hiding components in the belly, and a squared thrust vectoring exhaust to disperse the heat.

They use multiple angles on the fuselage to diffuse radar, interior mounted missiles or bombs, changed the intake to hide the compressor from radar, and a radar that can be aimed to reduce exposure.

One of the many ways to locate and identify an aircraft is by homing in on it's radar emission.

Radar absorbent coatings are employed to help reduce it's signature as well.