To execute a T-Spin, a player must first build a T-Tetrimino-shaped hole in the Matrix (called a T-Slot) with 1 extra block hanging over one side of it. There are tons of ways to build up this situation; the best way to practice building up the T-Tetrimino-shaped hole is to play the game in Marathon mode, this way there will be no time constraints and pressure on you.
As the T-Tetrimino falls, position it so that it is upright and so the cross of the T faces opposite from the overhanging block above the T-Slot. As the Tetrimino comes to rest inside the T-Slot, rotate it toward the open space under the block.
A T-Spin Single is the name for executing a T-Spin while clearing a single line, and a T-Spin Double is the reward using the T-spin move to clear 2 lines. T-Spin Triple is awarded for clearing 3-lines using this technique. Clearing lines with T-spin generates more points for normal play and lines sent in the case of multi-player games (Battle 2P and Battle 6P). Executing this move generates high rewards but poses a certain risk especially for T-spin double and triple as they tend to set up a structure in order to create back-to-back moves with it which might end up being Ko’ed if not done fast enough.
There are tons of ways to execute the T-spin move and it is up to the player’s style on how to build the setting for them. It will require practice and thinking ahead in order to properly deliver this move.
Here is an example from YouTube showing the power of T-spin: