Easy(ish)
Pull the black knob in the centre of the spool, it's spring loaded and will come off.
Poking the ends into the holes on the spool, wrap two separate lengths of strimmer line around the two separate recesses on the spool. The direction to wind them is shown by an arrow at the top of the spool.
Holding the lines in place poke the loose end of each strimmer line through the respective holes in the main body of the strimmer. Carefully push the spool back in place making sure that the lines are not tangled or snagged. Job Done. If it's in correctly, when the motor is running, the line should self feed if the spool is tapped on the ground.
Gordon Johnston
August 2008