hier
here
Refers to the place where the speaker is located.
Lass uns hier eine Pause machen, die Aussicht ist wunderschön.
Let's take a break here; the view is beautiful.

here
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here
Refers to the place where the speaker is located.
Lass uns hier eine Pause machen, die Aussicht ist wunderschön.
Let's take a break here; the view is beautiful.

The word 'hier' (here) can be combined with many prepositions to form pronominal adverbs (e.g., hier + mit = hiermit). These refer to something mentioned earlier or to the current situation.
Hierüber müssen wir später noch einmal sprechen.
We'll have to talk about this again later.
When 'hier' (here) is at the beginning of the sentence in position 1, the verb follows directly after it (inversion). However, it can also come after the verb and the subject to be less emphasized.
Hier ist das Rauchen verboten.
Smoking is prohibited here.
As a short answer to a question about attendance, for example from a list of names at school or university, you call out 'Hier!' (Here!/Present!). It is a fixed convention.
Der Lehrer rief meinen Namen und ich antwortete laut: 'Hier!'
The teacher called my name and I answered loudly: 'Here!'
When giving someone something, you can say 'Hier!' (Here!) or 'Hier, bitte!' (Here you go!). This is a typical utterance in spoken language, often accompanied by a gesture.
Hier, ich habe dir einen Kaffee mitgebracht.
Here, I brought you a coffee.
The expression 'hier und da' (here and there) means 'sometimes' or 'in various places'. The meaning is not literal, but expresses irregular frequency or distribution.
Ich habe hier und da ein paar Kratzer am Auto.
I have a few scratches here and there on the car.
there / since / then
'da' and 'hier' can both refer to a place or to someone's presence. 'hier' means the place where the speaker is right now. 'da' is more flexible: it can mean 'here' or 'there', depending on the situation, and it can also simply say that someone is present. Learners easily confuse the words because in some situations you may hear both. If you clearly mean your own location, 'hier' is more precise. 'da' fits when the place is already known or when the main point is presence.

Hier ist es ruhig, deshalb lerne ich gern in diesem Raum.
It is quiet here, so I like studying in this room.
Ist Frau Müller schon da?
Is Ms. Müller already there?