Using the verb GUSTAR 1

Gustar — the subject is the thing liked — The structure of gustar is the reverse of English. The thing liked is the grammatical subject: Me gusta el café (lit. Coffee pleases me). The person who likes it is the indirect object, marked by an IOP (me, te, le, nos, os, les). Always ask: what is pleasing whom?

Gusta vs gustan — agree with the subject — The verb agrees with the subject (the thing liked), not with the person: singular subject → gusta; plural subject → gustan. Me gusta el libro. Me gustan los libros. Me gusta bailar (infinitive is always singular). The IOP never changes regardless of singular/plural.

Clarifying le and les with a — Since le/les can mean to him, her, you, or them, add a clarifying phrase with a: A Juan le gusta el café. A mí me encanta. A ellos no les interesa. This phrase is optional when context is clear but very natural in speech — it's not redundant, it's emphasis.