Next time you are doing a swim workout, pay attention to your hands as they move under your body. As your hands start the pull, peek at them or watch them while the move into the catch position. Do yo see a lot of white foam around them? A lot of air bubbles? Or do you see plan old water and hands, no bubbles? If you don't see any bubbles, you don't need to read any further, you are already getting rid of the air before you pull - well done!
What's wrong with those air bubbles while you swim?
When you have a lot of bubbles on your hand while you swim, your hand is slipping thorugh the water. You are not getting hte most out of every pull or stroke. If you have ever seen a motor boat propeler suddenly spin faster when it rises out of the wate and then drops back in, with a lot of bubbly foam coing off of it, it is cavitating. That caviation means it is trying to spin air instead of water. Boat propelrers don't work well in the air. Your hand is not exactly a propeler, but the same thought applies. If you want to swim faster, you need to pull water with your hands, not air bubbles.
What causes those bubbles when you are swimming?
When your hand enters the water you pull some air in with you. Every swimmer does. Unles you enter the water so slowly and delicatly that your motion practically stops. you are going to have air bubbles on your hand after you enter the water. The air clings to your skin as your hand and arm enter and extend in front of you. It does not matter if you enter near your head and reach forward underwater or you enter with a fully extended arm - or anything in-between - air is going to go in the water on your hand.
How can I get rid of those bubbles while I am swimming?
This the trick. This is what you have to do to get rid of those air bubbles. After you enter the water and extend your arm, before you start to pull or press in the water, before you move your arm into the swimming catch position with a high vertical forearm, slow down. Wait. Pause. Give the bubbles a chacne to leave your hand before you move your hand any deeper in the water. Enter, extend, pause, then catch, press, and pull. Some people twist their hand a bit, some open and close their fingers a bit, but all of them have a slight pause to shed the bubbles.
Next time you are swimming freestyle, watch your pull pattern. Try to slow your hand at the start of the stroke next time you are trying to swim fast. I bet you will learn how to lose the bubbles and swim faster.