Ich schließe meinen Mantel, bevor ich nach draußen gehe.

Because Mantel is the direct object of schließen, so it has to be in the accusative case.

• nominative: mein Mantel = my coat
• accusative: meinen Mantel = my coat (as the thing being acted on)

In this sentence, I am doing something to the coat, so German uses the accusative:

• Ich schließe meinen Mantel.

This is a very common pattern in German:

• Ich sehe meinen Freund.
• Ich öffne die Tür.
• Ich nehme den Bus.

Here, schließe means something like close, fasten, zip up, or button up, depending on the coat.

The verb is schließen, which often means to close:

• die Tür schließen = to close the door
• ein Fenster schließen = to close a window

With clothing, it means closing or fastening it:

• den Mantel schließen = to close/button/zip up the coat

So it does not mean to lock here, and it does not mean to finish.

Because bevor introduces a subordinate clause, and in German subordinate clauses the conjugated verb usually goes to the end.

Main clause:

• Ich schließe meinen Mantel

Subordinate clause:

• bevor ich nach draußen gehe

That final position of gehe is completely normal after words like:

• bevor = before
• weil = because
• dass = that
• wenn = if/when

Compare:

• Ich esse, bevor ich arbeite.
• Ich bleibe zu Hause, weil ich krank bin.

In German, subordinate clauses are normally separated from the main clause by a comma.

So when you have:

• main clause + bevor clause

you write:

• Ich schließe meinen Mantel, bevor ich nach draußen gehe.

This is standard German punctuation. In English, people are often less strict with commas, but in German this comma is expected.

Nach draußen means outside in the sense of going out or moving to the outside.

That is important: it expresses direction, not location.

• Ich gehe nach draußen. = I go outside.
• Ich bin draußen. = I am outside.

So:

• draußen = outside, outdoors (location)
• nach draußen = to outside / outsideward (movement)

In this sentence, the speaker is moving from inside to outside, so nach draußen is the natural choice.

Because German normally needs an explicit subject in each clause.

So even though English also says before I go outside, learners sometimes wonder whether German can leave out the second I. It usually cannot here.

You need:

• Ich schließe meinen Mantel, bevor ich nach draußen gehe.

Not:

• Ich schließe meinen Mantel, bevor nach draußen gehe.

Each clause needs its own subject and verb.

Yes. German very often uses the present tense to talk about the near future, especially when the time is clear from the context.

So:

• Ich schließe meinen Mantel, bevor ich nach draußen gehe.

can refer to something happening now or about to happen.

German does have a future tense (ich werde gehen), but it is often unnecessary. Present tense is much more common in everyday speech when the meaning is obvious.

Yes, absolutely. That version is very natural.

When the bevor clause comes first, the main clause follows with verb-first word order after the comma:

• Bevor ich nach draußen gehe, schließe ich meinen Mantel.

Notice that you do not say:

• Bevor ich nach draußen gehe, ich schließe meinen Mantel.

That would be wrong, because in German the verb comes first in the main clause after an introductory element.

Yes, in many situations you can. Ich mache meinen Mantel zu is a very common, everyday way to say I do up / zip up / button up my coat.

Compare:

• Ich schließe meinen Mantel.
  Slightly more formal or neutral; perfectly correct.

• Ich mache meinen Mantel zu.
  Very common in everyday spoken German.

The second version uses the separable verb zumachen:

• Ich mache meinen Mantel zu.
• ..., bevor ich nach draußen gehe.

Because schließen works differently from anziehen.

With anziehen for clothes, German often uses a dative pronoun:

• Ich ziehe mir den Mantel an. = I put my coat on.

But with schließen, the coat itself is just the direct object:

• Ich schließe meinen Mantel.

You are not emphasizing putting the coat onto yourself; you are emphasizing fastening/closing the coat.

So:

• anziehen = put on
• schließen / zumachen = fasten, close, zip up, button up

In everyday German, Mantel usually means coat, especially an outer coat.

It can also mean covering or outer layer in other contexts, but in a sentence like this, learners should understand it as coat.

Common related words:

• der Mantel = coat
• die Jacke = jacket
• der Reißverschluss = zipper
• der Knopf = button

So the sentence gives a strong image of someone fastening their outer coat before going outside.

No. After bevor, you get subordinate clause word order, which means the verb goes to the end.

So the correct pattern is:

• bevor ich nach draußen gehe

not:

• bevor ich gehe nach draußen

That second version sounds like English word order and is not correct in standard German.

A good rule is:

• After bevor, put the subject first and the conjugated verb at the end.

Yes: the combination nach draußen gehen is very idiomatic and common.

German speakers often use:

• rausgehen
• nach draußen gehen
• nach draußen kommen

So this sentence sounds natural and everyday. It is also a nice example of how German often prefers a simple present tense and a subordinate clause with final verb placement.

Overall structure:

• Ich schließe meinen Mantel = main clause
• bevor ich nach draußen gehe = subordinate clause with bevor

It is a very typical, useful German sentence pattern.