This idea of this drill is to get used to the sensation of being on your side and start the body rotation process for when you swim freestyle. The easiest way to do something is to break it down into small sections.
So with that in mind this would be a good drill to start with as it’s a fairly simple drill to do. If you have to you could use a kick board to support you upper body and fins if you like (but try not to use them too much). To start you place your hand over the board with your hand at the top and the board supporting your forearm, stretch your arm out so that your shoulder (deltoid muscle) is against your ear and your other arm by your side. Hold this position for the whole lap so that your body is parallel to the wall of the pool, and once you get the end of the pool swap arms and go back.
A more advanced version of this drill if you removed your fins and try to repeat the drill with same position.
Then the next step up would be to remove the kick board and repeat the drill again in the same position.