Learn Spanish (Latin America): Al niño le gusta dibujar en el papel.

In Spanish, the verb gustar actually means "to be pleasing to." So, this sentence literally means "To the boy, drawing on the paper is pleasing." The word al is a mandatory contraction of a (to) and el (the). You must use a before the person who is doing the liking.

If al niño already means "to the boy," why do we also need le?

Spanish has a quirky rule: when you use a verb like gustar, you must include the indirect object pronoun (le, meaning "to him" or "to her"), even if you just named the person! Adding al niño at the start just clarifies exactly who le is referring to.

Why is it gusta instead of gustan?

The verb gustar matches what is being liked, not the person who likes it. When you like doing an action—which is represented by an infinitive verb like dibujar (to draw)—you always use the singular form gusta.

Does en mean "in" or "on"?

It means both! The Spanish word en is a very handy preposition that can mean "in," "on," or "at" depending on the context. Since you draw "on" paper in English, en el papel translates perfectly to "on the paper" here.