Start by putting a little potpourri in the bottom of the jar, then add some of the lights trying to push them towards the sides, then a little more potpourri, then more lights etc. until you have all your lights in and your jar is filled almost to the top with potpourri on top.
Now you need to center your doily on top of the jar and glue it all around with your glue gun.
As the potpourri gets warmed by the lights it will smell wonderful. Please keep in mind however, that if left plugged in too long the jar and potpourri can get very hot. Do not leave unattended and do not pick up the jar after it has been on a while without using an oven mitt to protect your hand.