3D Tic-Tac-Toe is similar in concept to traditional tic-tac-toe but is played in a cubical array of cells, usually 4x4x4. Players take turns placing their markers in blank cells in the array. The first player to achieve four of their own markers in a row wins. The winning row can be horizontal, vertical, or diagonal on a single board as in regular tic-tac-toe, or vertically in a column, or a diagonal line through four boards.
To master the game you'll have to learn develop a board situation where placing a mark on the board you create several (two or more) opportunities to make 4 in a row an the next move, so that the opponent can block only one of them. This situation has a name in japanese boarg games: ATARI.