If you are inserting a predefined way point to the flightplan, it will be automatically put to the end of the list of checkpoints.
To insert a predefined way point at any place in the flightplan you may use drag'n'drop technique.
Let's say you've planned a flight starting from LFPG (Charles De Gaulle, Paris, France) to EFHK (Helsinki, Finland).
Now you just decided to make a stopover in EDDH (Hamburg, Germany). Do it like this:
1. Insert EDDH, selecting it from the list of predefined way points. EDDH is put at the end.
2. Put the cursor over the left, grey area of the checkpoint field until the cursor changes its shape:
3. Left-click on the item, keep pressing down the mouse button while you drag the complete checkpoint field upwards.
4. Release the left mouse button as soon as the dragged field is in the right position:
Hint: This drag'n'drop technique is available for any checkpoint, as well as for the com and nav frequencies in the calculated flight plan.