to tongue a note you pronounce 'Tah' or something similar.
Triple tonguing is pronouncing 'Tah Kah Dah' or something similar.
It uses the tongue to accent three times before moving back to accent with the tip of the mouth. The 'Kah' and 'Dah' are normally weaker as you spend all your time playing 'Tah' You can get around this by practicing your scales for a few weeks on 'Kah' and 'Dah' articulations.
You would use it when playing quavers very fast in something like 6/8, 9/8 or 12/8 music. Triplets in 2/4 4/4 etc.
Triple tonguing is only really to be used after having learnt a strong double tongue.
Also I don't think this is really beginners stuff. It's pretty darn hard and takes time as you have to build up the muscles in your tongue gradually, and your tongue has to learn how to move in this way.