قبل أن نبدأ الرحلة، أضع الخريطة في الحقيبة.

Because قبل by itself usually comes before a noun, while قبل أن is used before a verb.

• قبل الرحلة = before the trip
• قبل أن نبدأ الرحلة = before we start the trip

So أن is what lets قبل introduce a whole verbal clause.

Here أن is a particle that is followed by a present-tense verb and turns it into a subordinated clause.

In this sentence:

• أن نبدأ = that we begin / to begin / we begin in a dependent clause

After words like قبل and بعد, this structure is very common:

• قبل أن... = before ...
• بعد أن... = after ...

So قبل أن نبدأ الرحلة literally has the structure before [we begin the trip].

Yes. After أن, the present-tense verb is normally in the subjunctive mood in MSA.

So the fully vowelled form would be:

• نبدأُ in the normal indicative
• نبدأَ after أن

In everyday unvowelled writing, both usually look the same: نبدأ.
That is why learners often do not see the change unless the text is fully vocalized.

Because Arabic verbs already include the subject.

• نبدأ = we begin
• أضع = I put

So Arabic often does not need separate subject pronouns like نحن or أنا unless the speaker wants extra emphasis or contrast.

For example:

• أضع الخريطة = I put the map
• أنا أضع الخريطة = I am the one who puts the map or I put the map with emphasis

In MSA, the present tense can cover several meanings depending on context, including:

• present habitual action
• near future
• planned action

So أضع الخريطة في الحقيبة can naturally mean something like:

• I put the map in the bag
• I am putting the map in the bag
• I will put the map in the bag

If the speaker wants to make the future very explicit, they could say:

• سأضع الخريطة في الحقيبة
• سوف أضع الخريطة في الحقيبة

Both mean I will put the map in the bag.

Because it refers to a specific trip, not just any trip.

• رحلة = a trip
• الرحلة = the trip

Arabic often uses the definite article ال when the noun is already known from context. In this sentence, the speaker and listener apparently know which trip is being discussed.

For the same reason: they are treated as specific, identifiable things.

• الخريطة = the map
• الحقيبة = the bag

This suggests the speaker has a particular map and a particular bag in mind. If you wanted the meaning a map or a bag, you would normally use the indefinite forms:

• خريطة
• حقيبة

If fully vowelled, the sentence would be:

قَبْلَ أَنْ نَبْدَأَ الرِّحْلَةَ، أَضَعُ الْخَرِيطَةَ فِي الْحَقِيبَةِ.

The important endings are:

• قبلَ: a time adverb expression
• نبدأَ: subjunctive after أن
• الرحلةَ: accusative, because it is the direct object of نبدأ
• أضعُ: indicative present
• الخريطةَ: accusative, because it is the direct object of أضع
• الحقيبةِ: genitive, because it comes after the preposition في

In normal Arabic writing, these short vowels are usually omitted, so learners have to infer them from grammar.

Because it comes after the preposition في, meaning in.

In Arabic, nouns after prepositions are normally in the genitive case. So:

• في الحقيبةِ = in the bag

This is a very common pattern:

• في البيتِ = in the house
• على الطاولةِ = on the table
• من المدرسةِ = from the school

This is because وضع is a verb whose first root letter is و, and in the present tense this و drops in the basic pattern.

So you get:

• past: وضعَ = he put
• present: يضعُ = he puts
• present, 1st person: أضعُ = I put
• present, 1st person plural: نضعُ = we put

This is a common pattern for some Form I verbs with an initial و.

It is not completely fixed. Arabic allows some flexibility.

This sentence begins with the time clause:

• قبل أن نبدأ الرحلة، أضع الخريطة في الحقيبة.

That order emphasizes the timing: before we start the trip.

You could also place it later:

• أضع الخريطة في الحقيبة قبل أن نبدأ الرحلة.

That is also natural. The meaning stays basically the same, but the focus shifts slightly.

A careful MSA reading would be:

qabla ʾan nabdaʾa ar-riḥlata, ʾaḍaʿu al-kharīṭata fī al-ḥaqībati

A few pronunciation notes:

• أ marks a glottal stop at the start
• ض in أضع is an emphatic consonant
• ح in الحقيبة is a strong breathy h, not the ordinary English h
• خ in الخريطة is like the ch in Scottish loch or German Bach
• the ة at the end of words like الخريطة and الحقيبة is pronounced as -a / -ah when pausing, but its case ending appears in fully read MSA

So in careful reading, the endings are heard, but in pausal pronunciation they are often reduced or dropped.