Usar vs. llevar vs. llevar puesto

In the Spanish language, 'usar', 'llevar' and 'llevar puesto' can all refer to wearing clothes, but they are used slightly differently depending on the context and region.

Usar

'Usar' translates directly to 'use' in English, and it can mean 'to wear' in the sense of using an item of clothing.
Ella suele usar vestidos en verano.
(She usually wears dresses in the summer.)
¿Usas gafas de sol cuando hace sol?
(Do you wear sunglasses when it's sunny?)

Llevar

'Llevar' typically means 'to carry' or 'to bring', but when talking about clothes it can also mean 'to wear'. It is used more flexibly than 'usar'.
Hoy llevo pantalones rojos.
(Today I'm wearing red pants.)
Mi hermana siempre lleva una chaqueta negra.
(My sister always wears a black jacket.)

Llevar puesto

'Llevar puesto' strictly refers to 'wearing something at the moment'. It translates into English as 'to have something on'. It is less versatile than either 'usar' or 'llevar'.
Ahora mismo llevo puesto un suéter porque hace frío.
(Right now I have a sweater on because it's cold.)
¿Cuándo llevas puesta esa camisa?, se te ve muy bien.
(When did you put that shirt on? It looks really good on you.)

Summary

Although all three words ('usar', 'llevar' and 'llevar puesto') can be translated into English as 'to wear', their usage differs. 'Usar' is like using an item of clothing, just as you might use any object. 'Llevar' is a broader term that can cover wearing clothes, and implies carrying or having clothing with you. In contrast, 'llevar puesto' specifically refers to what you're wearing at the time of speaking.