Basically, tonguing means touching the reed with the tongue quickly to stop the vibration, and therefore the sound. My best practice technique for tonguing is to play one note, and breaking it into several short tones by saying to-to-to-to-to-to-to-to-to against the reed. Do this as quickly as you can without getting a sloppy sound, and do this on every note of the scale during warmups. When you quicken up your tongue, you'll be able to learn to coordinate the tonguing with the changing of the notes as well. There are double-tonguing techniques for saxophone as well, but you should work on quick single-tonguing first. It is cleaner. Good luck. (And I echo the previous response: Practice, practice, practice! :-) )