Nous prenons le tram pour aller au centre-ville.

In French, when you talk about using a means of transport as a direct object, you almost always use prendre (to take):

• prendre le tram – to take the tram
• prendre le bus – to take the bus
• prendre le train – to take the train

You cannot say nous allons le tram. The verb aller (to go) is not used with a direct object like that.

If you want to use aller, you must change the structure:

• Nous allons en tram au centre-ville. – We go by tram to the town centre.

So:

• Nous prenons le tram = We take the tram.
• Nous allons en tram = We go by tram.

Both are correct French but use different verbs and prepositions.

Prenons is the correct present-tense form of prendre with nous.

Prendre (present tense) is irregular:

• je prends
• tu prends
• il / elle / on prend
• nous prenons
• vous prenez
• ils / elles prennent

So the pattern with nous is -ons, but the stem changes to pren-, not prend-.
That is why it is nous prenons, never nous prendons.

Yes.

• Nous prenons le tram… is more formal or neutral.
• On prend le tram… is very common in everyday spoken French.

In modern spoken French, on often replaces nous and usually means we.
The verb form changes:

• nous prenons → on prend

Both sentences mean the same thing; the choice is mostly about register (formal vs casual).

Yes, le tram is a shortened, informal form of le tramway. Both refer to a tram / streetcar.

• le tramway – the full word
• le tram – shorter, very common in everyday speech

Grammatically they behave the same way:

• prendre le tram / le tramway
• attendre le tram / le tramway

You must use an article; Nous prenons tram is incorrect.

In French, nouns usually need an article (definite, indefinite, or partitive). With means of transport and prendre, the definite article le / la / les is very common:

• prendre le tram
• prendre le bus
• prendre le métro
• prendre la voiture

You would change the article only if you want to change the meaning:

• Nous prenons un tram. – We take a tram (one tram, not specified).
• Nous prenons le tram. – We take the tram (a specific or habitual tram line / mode).

Both relate to using the tram, but the structure and nuance differ:

• prendre le tram

  • Verb: prendre
  • Object: le tram
  • Focus: the action of taking that particular means of transport.
  • Example: Nous prenons le tram pour aller au centre-ville.

• aller en tram

  • Verb: aller
  • Preposition: en
    • means of transport
  • Focus: how you go (by tram), more like English “go by tram”.
  • Example: Nous allons en tram au centre-ville.

Both are correct. In your sentence, the speaker chose the prendre + direct object pattern.

After pour to express purpose (in order to), French uses the infinitive, not a conjugated verb:

• pour aller – to go / in order to go
• pour manger – to eat / in order to eat
• pour comprendre – to understand / in order to understand

So:

• Nous prenons le tram pour aller au centre-ville.
  literally: We take the tram in order to go to the town centre.

Pour allons or pour nous allons is always incorrect.
Correct pattern: pour + infinitive (aller, manger, voir, etc.).

Yes, but the tone changes slightly.

• pour aller – very common, neutral, used in all kinds of French.
• afin d’aller – more formal or written, means the same thing: in order to go.

So you could say:

• Nous prenons le tram afin d’aller au centre-ville.

This is correct, just a bit more formal or careful in style.

Au is the contraction of à + le:

• à + le = au
• à + les = aux

Because centre-ville is masculine singular (le centre-ville), à le centre-ville contracts to au centre-ville.

Examples:

• au centre-ville – to the town centre
• au parc – to the park
• aux magasins – to the shops

So the rule is grammatical, not special to centre-ville.

Centre-ville is a compound noun written with a hyphen:

• le centre-ville – the town/city centre (as a fixed concept or area)

You can also say:

• le centre de la ville – literally the centre of the city/town

Both are correct and usually mean the same place.
Le centre-ville is shorter and more idiomatic as a place name; le centre de la ville sounds a bit more descriptive or literal.

Centre-ville is masculine:

• le centre-ville
• au centre-ville (because à + le = au)
• du centre-ville (because de + le = du)

Grammatically, the gender comes from centre, which is masculine (le centre).
Ville is feminine (la ville), but in the compound centre-ville, the head noun is centre, so the whole compound is masculine.

In French, the present tense can express both:

1. An action happening now:

   • Nous prenons le tram pour aller au centre-ville.
     → We’re taking the tram (right now) to go downtown.

2. A habitual action:

   • Nous prenons le tram pour aller au centre-ville.
     → We take the tram (whenever we go) to go downtown.

Context decides which meaning is intended.
French usually does not need a separate progressive form like “are taking”; the simple present prenons covers both.