The verb combinar [kome-bee-nar] has a number of meanings, but we’re going to focus on the three main ones.

1. Making plans

Vamos combinar para sair na sexta-feira. Let’s make plans to go out on Friday.
Já combinei com ela. I already made plans with her.

Along these lines we can also say:
Combinado! Agreed!

2. Corresponding/matching

Neste exercício, tem que combinar o desenho com a palavra correta. In this exercise, you have to match the drawing to the correct word.

3. Matching (clothes, jewelery, etc)

Essa camisa combina com sua calça. That shirt matches your pants.

Olha essas Havaianas. Combinam com seu cabelo, combinam com seus olhos, seu sorriso, com sua canga. Look at those flip flops. They match your hair, they match your eyes, your smile, and your beach wrap.

To take a closer look at this usage, let’s look at this Havaianas commercial (the snippet above is used in the commercial):