Well first you get a net to catch them in, then you will find what place to catch the turtles at. Then after you do that you will look for heads sticking up or if you see bubbles then if you see one you get the net ready and swipe where you saw it.
Well, It depends on where you are at. I am in MI, so the main way I do it would be to walk up and down the dock over and over again. Eventually they get used to my being there and with a PVC pipe-lenghtend net I dip it under them or throw it overthem depending on their distance.
If your in tn you can go to tims ford lake there just about everywhere
I caught one today in a pond by using a smaller stick to pull the log the turtle was on near me and the put a bucket in front of it and it climed in