Start kicking on side, head down eyes looking to the bottom, count to 6. One arm out in front, other arm on hip. Lift arm on hip and enter it into the water finger tips first parallel to the spare arm. As your finger tips touch the water, the arm in front catches the water and pushes it back. As you push back turn the head and body towards the pushing arm and breathe in. It's like the arm pushing back opens a window for you to breathe into. You then have a new arm out in front, and different arm on hip. Breathe in and when you are ready go again. Mantra for this is head in and count, lift arm and enter, turn and breathe.
The goal is to not let the lead arm move until the other arm enters. if you struggle with this grab a berroca tube and hold it out in front and swap hands as the hadn't enters. Having something physical to hold can really help. The counting is so that you are ready to breathe in as soon as you swap sides. This helps you breathe at the correct time and this drill helps you breathe on both sides. Something super important when you want to swim in the ocean or have balance in your stroke. You wouldn't go to the Gym and just work out on your left