"Das ist dein Lehrer."

Translation: This is your teacher.

[ArmasUkkoM]

"Die" or "der" are definite articles and need in general a special context, which has been made clear before to be grammatically correct. In this sentence however, a new information is introduced, so we cannot refer to something already been mentioned. That's why we need "Das" and not "Der" or "Die".

[Arth__29]

Is there some difference when i use "That" and "This", is German?

[GuardianCiego]

No, as far as I know. In fact, they use additional particles like 'that over there' das da to help differenciate.

[nxexa89]

Dies und das = this and that

[jfinley6]

Can someone explain why you would use das for "that" and not something like "die" or "der"?

[GuardianCiego]

the demonstrative pronoun 'this' / 'that' just happens to be spelled like the article 'das'. Consider it a coincidence to help remember

[Mustafa-Abbas]

Why is it not " deinen Lehrer"?

[GuardianCiego]

Because this is nominative case, where the singular triplet is <dein, deine, dein>.

<deinen, deine, dein> belongs to accusative (that is, when it is direct object) as in I have your dog (ich habe deinen Hund).

[lewisuan]

Is Lehrer have some relation with leader?