Hi.
"De" and "het" mean exactly the same thing, "the" in English. The usage depends on the gender of the word. I see you're also learning German, you have genders in German too.
de = masculine and feminine, no distinction between these two genders (der and die in German)
de man (der Mann) = the man
de vrouw (die Frau) = the woman
het = neutral (das in German)
het kind (das Kind) = the child
het oog (das Auge) = the eye