Learn Spanish (Spain): El cliente quiere relajarse aquí.

When you have a conjugated verb (quiere) followed by an infinitive (relajar), you can attach the reflexive pronoun (se) directly to the end of the infinitive to make one single word: relajarse. You could also place the pronoun before the conjugated verb: El cliente se quiere relajar aquí. Both ways are perfectly correct!

Why do we need the se? Can't we just say quiere relajar?

In Spanish, relajar by itself means to relax something else, like a tight muscle, or to calm another person down. When someone is relaxing themselves, you must use the reflexive form relajarse.

Why is the verb quiere instead of quere?

Querer (to want) is a stem-changing verb. This means that for most subjects, the e in the middle of the word changes to ie. Because el cliente acts as a third-person singular subject (like he or she), the verb changes to quiere.

Where would I put an adverb ending in -mente if I wanted to describe how he relaxes?

If you wanted to add an adverb of manner from this current lesson, such as tranquilamente (peacefully), it naturally goes right after the verb it describes. You would say: El cliente quiere relajarse tranquilamente aquí.