On the left side of the HUD is a ladder showing your current airspeed in nautical miles per hour (it displays true airspeed). Above that, in the upper left corner, is a G-meter.
The right ladder shows altitude; above that is a readout of your current angle-of-attack in degrees ("a=X.X"). Your jet will stall at a 30 degrees positive angle of attack and negative 16 degrees.
The airplane symbol (something like "-O-") shows the direction that the relative wind is coming from. The relative wind combines your current angles of attack and sideslip. A ladder in the center of the HUD show your aircraft's current attitude.
The lower, horizontal ladder shows your current heading. Discretes in the lower left-hand corner show the state of your weapons systems. Slightly above them is a readout of your current thrust percentage as well as the state of your engine's afterburner – the "AB" symbol means the afterburner is on.