The first thing you need to do is simply try and follow the leader. Your partner, who may or may not have formation flight experience, simply needs to use the "straight line" autopilot. (Accessed through the backspace key.) What you need to know to do this is called...
Iceman's visual speed rule:
Approach a flight lead at 50 to 40 knots faster than him. (The relative airspeed indicator on their username circle should read between -40 and -50, which means they are that many knots slower than you.) When you can see the outline of their aircraft, slow down to 20-30 knots faster than them. When you can see their exhaust nozzle clearly, slow down to 15 knots faster. And finally, when you can see the aircraft in a reasonable amount of detail, as well as their weapon configuration, slow down to five knots slower. Once you are within a holding pattern like the basic echelon, stay at the same relative and heading. (+0 or -0 indicated) Try to make the formation as tight as possible, and don't go in front of your leader! (overshoot)
Congratulations, you are now flying in your first aircraft formation! Getting good at it is pretty tough. However given enough time, you will be able to perform formation aerobatics, with smoke and all that jazz. Just keep at it!
here are some of the basic formation patterns to practice (relative height portrayed by size change, the smaller it is the lower it is)
This formation below is also referred to as the Line Abreast formation.
