You fill the expansion tank up to the top mark.
Open the coolant bleed bolt (on the thermostat housing).
You then fill the radiator up until you can see the coolant at the bottom of the filler neck and water is running out the bleed bolt in a steady stream (no bubbles). Tighten the bleed bolt.
With the radiator cap off, start the engine and let it run until warmed up (fan comes on). If necessary, top up radiator to base of filler neck.
Turn the engine off and replace the cap. Turn the engine back on and run for a shortwhile to check for leaks. Put the heater on full heat, full blast while running now.
Thats it

Also make sure you use a 50/50 mixture! Not just water.