قبل أن أخرج من البيت، أضع البطاقة في الحقيبة.

Because قبل by itself is usually followed by a noun or a verbal noun, not a full finite verb clause.

• قبل أن أخرج = before I leave / before I go out
• قبل الخروج = before leaving
• قبل خروجي = before my leaving

So when Arabic wants to say before + subject + verb, it commonly uses قبل أن + imperfect verb.

Yes. After أن, Arabic normally uses the imperfect verb, but in the subjunctive mood.

So here:

• basic imperfect: أخرجُ = I go out / I leave
• after أن: أخرجَ

In normal unvocalized writing, both are written أخرج, so you only see the difference if vowel endings are written.

In this sentence, أن أخرج means that I leave / that I go out, and after قبل it gives the meaning before I leave.

Arabic uses the imperfect for several meanings, including:

• present actions
• habitual actions
• near-future actions, depending on context

In this sentence, أضع البطاقة في الحقيبة most naturally sounds habitual:

• Before I leave the house, I put the card in the bag.

If you wanted to make a specific future meaning clearer, you could say:

• سأضع البطاقة في الحقيبة = I will put the card in the bag

So as written, the sentence is best understood as a routine or regular action.

Because the verb already tells you the subject.

In both أخرج and أضع, the initial أ marks first person singular:

• أخرج = I leave / I go out
• أضع = I put

Arabic often leaves out subject pronouns when the verb already makes the subject clear.
You could add أنا, but that would usually give emphasis:

• أنا أضع البطاقة... = I put the card... / I am the one who puts the card...

Because with the verb خرج, Arabic normally uses من to express the place you are leaving:

• خرج من البيت = he went out of the house
• أخرج من البيت = I go out of the house / I leave the house

This is the standard pattern: خرج من ...

So من is not optional here; it is the natural preposition with this verb when you mention the place you are leaving.

Because وضع usually takes في when you mean putting something inside something.

• أضع البطاقة في الحقيبة = I put the card in the bag

Here في describes the resulting location: the card ends up in the bag.

Using إلى would mean to/toward, which is not the normal choice with put in this context.

They are the definite article, like the in English.

So:

• البيت = the house
• البطاقة = the card
• الحقيبة = the bag

This suggests the speaker means a specific house, card, and bag, not just any house/card/bag.

If you wanted them to be indefinite, you would remove الـ, for example:

• بطاقة = a card
• حقيبة = a bag

In normal Arabic writing, short vowel endings are usually omitted, but they are still understood grammatically.

A fully vocalized version would be:

قَبْلَ أَنْ أَخْرُجَ مِنَ الْبَيْتِ، أَضَعُ الْبِطَاقَةَ فِي الْحَقِيبَةِ.

Important endings here:

• أخرجَ: subjunctive after أن
• أضعُ: indicative in the main clause
• البطاقةَ: accusative, because it is the direct object
• البيتِ: genitive, because it comes after من
• الحقيبةِ: genitive, because it comes after في

So even when the endings are not written, the grammar is still there.

Yes. Arabic word order is flexible.

This sentence:

• قبل أن أخرج من البيت، أضع البطاقة في الحقيبة.

could also be said as:

• أضع البطاقة في الحقيبة قبل أن أخرج من البيت.

Both are correct. The difference is mostly about focus and style:

• putting قبل أن أخرج من البيت first emphasizes the time relationship
• putting أضع البطاقة في الحقيبة first emphasizes the action itself

Yes. Arabic can also use a verbal noun or a noun phrase instead of أن + verb.

For example:

• قبل الخروج من البيت، أضع البطاقة في الحقيبة.
• قبل خروجي من البيت، أضع البطاقة في الحقيبة.

These mean roughly the same thing:

• Before leaving the house, I put the card in the bag.
• Before my leaving the house, I put the card in the bag.

So:

• قبل أن أخرج = more directly before I leave
• قبل الخروج / قبل خروجي = more like before leaving / before my leaving

All are natural, but قبل أن أخرج is often especially clear for learners because it matches a full clause.