A flip turn is really easy to do. Here are a few simple steps for doing the turn:
STEP 1: Approach the wall of the pool swimming freestyle. Begin your turn just short of a body length away from the wall.
STEP 2: Tuck your chin to your chest and roll your body into a ball, so that you start to do a forward flip in the water. Blow air out of your nose to avoid inhaling water.
STEP 3: Open your body halfway through your flip and extend your legs to push off against the wall.
STEP 4: Push off the wall in the opposite direction from the one in which you were swimming. You should still be on your back at this point.
STEP 5: Streamline your entire body and roll back over onto your belly as you glide. Your shoulders should be up against your ears and your fingers should be pointed. Begin kicking immediately.
STEP 6: Begin stroking with your arms as soon as your body breaks the surface of the water.
There are a lot of ways you can practice a flip turn as well. Start by doing flips in the middle of the pool. Don't worry about exiting the "ball" position.
Once you've got the hang of that, start to open up the ball. You should almost be sitting, legs bent to about 90 degrees. Keep practicing.
Ready for the wall? This time stand in front of the wall, then flip.
Don't push off the wall. Simply stop your flip once your feet touch the wall. Repeat until you feel well acquainted with where the wall is and where you should be once you begin your flip.
Now that you have gotten a feel for using the wall, stand a couple feet back, and then jump into your turn, pushing off on your back. Remember your technique!
After practicing that for a while, start to swim into the wall. Don't breath for two strokes into and out of the wall. Also, make sure you are pushing off on your back. Don't twist around on the wall. Believe me, it pays to develop good habits early on.
Well that's about it. A flip turn is very simple, it really just takes a ton of practice.
Steps from here.