The articles der, die, and das can also be used as demonstrative pronouns. In that case, they are almost always at the beginning of the sentence, and cannot be translated with „the“. See how they’re used to avoid repeating the noun by replacing it:

Wo ist das Geld? Das haben die Großkauf-Diebe!
Where is the money? The Großkauf Thieves have that!

We replace a man like Fritz with der, and a feminine noun like Anna with die, and things like “das Büro” with das. Demonstrative pronouns also put more emphasis on a person or thing:

Paul: Ja, und Fritz ist Polizist. Der hat viel Arbeit!
Yes, and Fritz is a policeman. That guy has a lot of work!

There is a similarity to the substitute pronouns from lesson 8. But those only mean „it“ in English, and don’t emphasize anything:

Der Computer? Er ist hier.
The computer? It is here.