A T square shows a dynamic where the planet that is in square to the opposition arbitrates the other two planets. The best way to learn how to deal with a T square is by looking at the opposite position of the square (the empty point). The sign where this empty point is located will show the best attitude towards this dynamic, as it balances it, removing the weight on the square planet.
A T square is a pattern of learning. People with T squares in their charts will display a desire of overcoming aspects of the Self that are in conflict, allowing expansion of consciousness.