The name of the C/T Trick comes from the default binds that are used for this technique.
C — Character Screen
T— Skill Tree
Of course, these binds should be changed. Personally, I have them as follows: "A" — CS, S — ST, but when playing Hdin I am lack of available binds, so I had to bind Fanaticism on "T", which is not very convenient. One of my friend's binds are as follows: "C" — CS and B — ST. So think of the binds yourself, so they would be comfortable for you.
The thing with this trick is that when you open certain game screens (Character screen and Skill Tree) we can increase the radius (more like the rectangle) of skills like Teleport and Lightning Sentry. Works with other skills as well, but unlike TP and LS they don't do much impact in the duel.
When pressing "C" (opening a CS) and using TP at the edge (the corner) of the screen, its length increases in half (length from right to left. the height does not increase).
Here is the beginning of the Teleport of Paladin and the distance at which you can stomp by pressing the Teleport at the left edge of the screen.
Now press TP at the edge of the screen when you opened CS.
That much more we have overflowed rather then we used normal TP
Here is a comparison. As I said, is roughly 1.5x more.
Also here a comparison of how farther can you TP by using C/T trick when doing 1(2) TP's.
It is also worth mentioning that when using C/T in the upper right (left) corner, the angle changes. White line ~parallel to the edge of the map. So, when you normally teleport in the right corner of the screen you will move left on to the line, and if C/T - slightly to the right.
By using C/T you can overrun your opponent even though your enemy has a higher breakpoint on TP, but he isn't using C/T. In this video Assassin (102fcr — 9 frames TP) is using C/T and overruns Necro (125fcr — 8 frames TP) who uses regular TP.
C/T is a very useful trick when playing as an Assassin and setting traps. Traps will be set 1.5x farther! Sometimes a Nec won't even expect that there are already traps set ahead of his way.
Go for it! In the beginning, I was all confused too. Either I opened a wrong window or forgot to close one. After a month, I had much of a progress. The confusion became less frequent. After 2-3 months I already made the trick automatically.
However, this does not mean that you should try to do every TP or Traps by using C/T. That way you will definitely get confused at some point (might be lethal). With some experience, you will know when you need to use C/T and when you don't. It is mainly used to catch someone up/quickly fly away/quickly fly and make unexpected stomp/to set traps on the way of a Necro (where he doesn't expect them to be or ahead of the way of a possible IBS).
It's also useful to use C/T to spam Teeth (the flow of the Teeth will be more concentrated and will likely cause more damage).
Good Luck and Have Fun!
Wish you good luck in all your endeavors!