You don't train a dog to track per say, you train him to find an item set down by you or someone else.  This is the one thing that he can do alone and you can't help him.   There are many theories to tracking, many books written, here is how I do it, I'm a beginner at this, what you will see is my learning experience, I apply it cause it works for me, but it might not work for you, every dog is different.