Use [WASD] to move selector. Use [F] to toggle the radar mode from {SCAN} to {LOCK}. Make sure that the radar beam is properly and fully illuminating the target. Use [SPACE] to launch a missile. The radar may lose lock during the missile's flight. If this happens, the missile will continue in the last direction it was flying, so re-illuminate the target with radar as soon as possible to reengage the missile's tracking system.
This is a (very unrealistic) simulator that tries to replicate the experience of being a Radar Intercept Officer (RIO) in a U.S. Navy McDonell Douglas F-4B Phantom II fighter-interceptor. The radar scope is a B-Scope connected to an APQ-72 all-weather radar system. The missile is (in theory) an AIM-7(E?) Sparrow. The Sparrow is a semi-active radar-guided air-to-air missile.