The subjunctive mood is used in a subordinate clause following the expression of an emotion or judgement.

sentir, alegrarse de, es bueno, es malo, es una lástima, es increíble, etc.

Without subordinate Clause - Infinitive
Me alegro de ganar.
I am happy to win.

With subordinate Clause - Subjunctive
Me alegro de que hayas ganado.
I am glad that you have won.

¡Qué suerte que se hayan encontrado después de tantos años!
How lucky for you to have found each other after so many years!

Me alegro de que Uds. puedan ir a la fiesta.
I am glad that you can go to the party.

Qué lastima que tu carro se haya descompuesto.
It's a shame that your car has broken down.

Es bueno que el coche tenga aire acondicionado.
It's good that the car has air conditioning.

Me enoja que nuestro carro use tanta gasolina.
It angers me that our car uses so much gas.