Question

With gustar you have two choices of conjugations: _______ and _______ (same with encantar) When do you use each of those?

Answer 1

With gustar you have two choices of conjugations: gusta and gustan (same with encantar) When do you use each of those?

Gusta is used for singular person or thing.
Me gusta la casa de mi abuela. La casa is singular.
A ellas les gusta el chocolate. El chocolate is singular.

Gusta is used before an infinitive verb
Te gusta comer pizza. It is used before an infinitive is always Gusta in singular.
A ellos no les gusta levantarse temprano. It is used before an infinitive is always Gusta in singular.

Gustan is used for plural persons or things.
Me gustan los vestidos rojos. Los vestidos is plural.
A ellos no les gustan las tareas de la escuela. Las tareas is plural

Never use gustan before the infinitive.
Te gustan comer pizzas. It is wrong Spanish grammar. Very bad.