Hello Osai J. Unlike English language, in Portuguese we use de definite article "THE - o, a, os, as" in front of a noun in general. O que = What Eu não entendi o que ela disse. - I didn´t understand what she said. Eu não sei o que fazer. - I don´t know what to do. Eu encontrei o que você estava procurando. - I´ve found what you were looking for. O que você gosta de assistir na TV? = What do you like to watch on TV? O que você faz nos finais de semana? = What do you do on the weekendes? O que a menina comprou no shopping center? - What did the girl buy in the mall? O menino é legal - The boy is nice. O sistema solar é bem complexo - The solar system is quite complex.

It depends on the sentence. Actually "o" can be a definite article and because of that we see it very often in Portuguese. For instance, when we say "the day is nice" we would use the "o": "O dia está bom",

"O que" means "what" What does it mean? = O que significa?