I am installing the frets in almost every slot, but not the first slot nor the 16th, Those slots will be filled later, but for now I need them open so I can drive a tiny brad through them to properly position the fretboard on the next when it comes to glueing it down.
First a little luthiers glue. This will be thinned and spread with a finger and then pounded and pressed into the sawn slot.
Here is the press, which drives the fret firmly into the slot. Much better than hammering them in.
The frets are glued pressed and dried. Now it is time to glue on the fretboard. Brads are driven through tiny holes in fret slot 1 and 16 to position the fretboard just right. Then they are pulled, glue applied and then those brads find their old holes in the neck, are driven deeper and clamps are tightened. An ancient but proven method.