Min frakke hænger bag døren, og jeg spænder mit bælte, før jeg sætter mig i bilen.

Because Danish nouns have grammatical gender.

• frakke is a common-gender noun, so you use min
• bælte is a neuter noun, so you use mit

So:

• min frakke = my coat
• mit bælte = my belt

This is very common in Danish:

• min bil
• min jakke
• mit hus
• mit bord

After a possessive like min, mit, din, hans, vores, and so on, Danish normally uses the indefinite form of the noun.

So:

• min frakke = my coat
• mit bælte = my belt

Not:

• min frakken
• mit bæltet

The idea is that the possessive already makes the noun definite in meaning, so Danish does not usually add the definite ending as well.

Because those nouns are not following a possessive. They are simply being referred to as specific, known things:

• døren = the door
• bilen = the car

In Danish, the definite article is often attached to the end of the noun:

• dør → døren
• bil → bilen

So the sentence is talking about a particular door and a particular car.

Bag is a preposition meaning behind.

So:

• bag døren = behind the door

Yes, bagved døren is also possible and also means behind the door. In many everyday contexts, bag døren is the simpler, more direct version.

So both can work, but bag døren is completely normal Danish.

They are all in the present tense.

In Danish, the present tense is usually formed with -r, and with verbs like these it appears as -er in spelling:

• at hænge → hænger
• at spænde → spænder
• at sætte → sætter

Also, Danish verbs do not change according to the subject the way English verbs sometimes do. So the same present-tense form is used with jeg, du, han, vi, etc.

It can cover both, depending on context.

So Danish hænger, spænder, sætter mig can correspond to English:

• hangs / is hanging
• fasten / am fastening
• sit down / am sitting down

Danish usually does not need a separate continuous form like English is hanging or am fastening. The ordinary present tense often does that job.

Because og is joining two full clauses, and the second clause needs its own subject.

Structure:

• Min frakke hænger bag døren
• og jeg spænder mit bælte

Even though English also repeats the subject here, learners sometimes expect Danish to drop it more easily. In this kind of sentence, repeating jeg is normal and correct.

Normally bælte by itself means a belt you wear around your waist.

If you mean a seat belt, Danish usually says:

• sikkerhedssele

So:

• jeg spænder mit bælte = I fasten my belt
• jeg spænder min sikkerhedssele = I fasten my seat belt

That is an important distinction.

Because at sætte sig is a reflexive expression meaning to sit down or to seat oneself.

• at sætte by itself usually means to set / put / place
• at sætte sig means to sit down

So:

• jeg sætter bogen på bordet = I put the book on the table
• jeg sætter mig i bilen = I sit down in the car / get into the car and sit down

The little word mig is necessary because the meaning changes.

Because mig is the object form of jeg.

Compare:

• jeg = I
• mig = me

In reflexive constructions like sætte sig, Danish uses the object form:

• jeg sætter mig
• du sætter dig
• han sætter sig

So jeg sætter jeg would be wrong.

Often, yes, in everyday meaning.

Literally, sætter mig i bilen is more like sit down in the car or seat myself in the car. But in normal use, it can easily correspond to English get into the car, especially if the focus is on the action of taking your place in it.

If you want a more direct get into the car, Danish can also use:

• jeg stiger ind i bilen
• jeg går ud i bilen in some contexts, though that is different in nuance

Still, jeg sætter mig i bilen is very natural.

Because Danish uses i for being inside an enclosed vehicle like a car.

So:

• i bilen = in the car

Using på bilen would mean on the car, physically on top of it or on its surface.

This matches English pretty closely:

• in the car
• on the car

Før means before and introduces a subordinate clause:

• før jeg sætter mig i bilen

A useful thing to notice is the word order. In this subordinate clause, Danish keeps the normal subject + verb order:

• jeg sætter mig

That is different from main-clause Danish, where verb-second word order is important.

Then the main clause would show normal Danish verb-second word order.

For example:

• Før jeg sætter mig i bilen, spænder jeg mit bælte.

Notice that after the fronted subordinate clause, Danish says spænder jeg, not jeg spænder.

That is a very common Danish pattern: fronted element + finite verb + subject.

There are two different reasons.

1. The comma before og separates two main clauses:

   • Min frakke hænger bag døren
   • og jeg spænder mit bælte

2. The comma before før is a start comma before a subordinate clause:

   • før jeg sætter mig i bilen

In modern Danish, that second comma is often optional, depending on the comma system being followed. So many writers would also accept:

• Min frakke hænger bag døren, og jeg spænder mit bælte før jeg sætter mig i bilen.

But the first comma, between the two full main clauses, is standard.

These are two vowels English speakers often struggle with.

• æ in hænger, spænder, sætter, bælte is roughly similar to the vowel in English cat, but not exactly the same
• ø in døren has no exact English equivalent; it is a front vowel said with rounded lips

A practical tip:

• for æ, think of a fairly open eh/a sound
• for ø, try saying an eh-type vowel while rounding your lips

You do not need perfect native pronunciation immediately, but it is worth noticing that these vowels help distinguish words in Danish.