If you have a good feel for what TSS is, or if you're OK with the mathematical definition of TSS and how TSS is calculated, then this article is not meant for you.
If you struggle with TSS because you can't really, in your gut, get a handle on exactly what it means then this article might help.
TSS is quite simply the best tool going for determining how you're going to feel tomorrow, and possibly the day after tomorrow, after today's effort.
What I'll suggest for understanding TSS is that you look at today's training effort, whether it's a race or a group ride or a trainer workout, as just so much work to be done. Work can be quantified easily enough. Riding from point A to point B might take, for instance, 1000kJ of work. The work you do in riding from point A to point B is done overcoming gravity and wind and rolling resistance.
TSS is a way of quantifying how you went about accomplishing that 1000kJ of work.
If I asked you to load a pile of bricks to load onto a truck, do you think that the manner in which you choose to load them will determine how you'll feel in the morning? Sure it does. You could load them by picking them up 10 at a time or 1 at a time. If you chose to load them 1 at a time at an easy pace, you probably won't feel too tired in the morning. You might not even feel too bad when you're done.
If you load them 10 at a time but take a nice long break between each 10, you might feel that tomorrow and you might not. Do them 10 at a time with little or no rest between loads...
See how this works? In each case the same amount of work was done. All the bricks are loaded. The rider went from point A to point B. The important difference is how that work was accomplished - was it done slowly or quickly, in large chunks or small ones.
TSS, simply defined, is a number that represents what sort of effect a given amount of work will have on you.