The subjunctive mood has many uses, two of those uses are to express feelings and to make a subjective judgement. The subjunctive is used in a subordinate clause following the expression of an emotion or judgement. Expressions, such as those shown below, require the use of the subjunctive in clauses they govern.

estar alegre, alegrarse de - to be happy
estar triste - to be sad
temer, tener miedo de - to fear, be afraid
esperar - to hope
sentir, dar lástima - to feel sorry, regret
gustar, agradar, encantar - to like, be pleased, be delighted
disgustar, desagradar - to dislike, be displeased
sorprender, estar sorprendido - to be surprised

Me alegra que usted esté satisfecho con la ayuda que recibió hoy.
I'm happy you are satisfied with the help you received today.

¿No te alegras de que Elisa y David sean tan felices?
Aren't you glad that Elisa and David are so happy?

Temo que ellos la hayan enojado demasiado.
I am afraid that they had gotten her too angry.

A ella le gusta que vayas a verla.
She likes that you go to see her

Me gusta que la habitación sea tranquila.
I like for the room to be quiet.

Nos disgusta que tú hayas olvidado la sombrilla.
We don't like that you have forgotten the sunshade.

No me sorprende que Carla tenga éxito.
It does not surprise me that Carla is successful.

Es bueno que lo dejes solo.
It's good that you leave him alone.

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.

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

Note: If the sentence does not contain a subordinate clause, one uses the infinitive.

Me alegro de ganar.
I am happy to win.