This is the 2925th most frequent Portuguese word.
los
"Los" is not Portuguese; it is Spanish and means "the" (masculine plural).
In this sentence, "los" is used as a pronoun referring to "the shoes," functioning as a direct object of the verb "ver." It is appended to the verb in its infinitive form, showing object pronoun usage.
Eu vou comprar aqueles sapatos, porque eu realmente gostei de vê-los.
I am going to buy those shoes because I really liked seeing them.
Here, "os" (shortened form of "los") directly precedes the conjugated verb "viu." It acts as the direct object pronoun replacing "them."
Você os viu na loja antes?
Did you see them at the store before?
In this usage, "los" is attached to the verb "comprá" in its infinitive form, serving again as a direct object pronoun referring back to "os sapatos" (the shoes).