Si nous partons trop tard, nous risquons de manquer le train.

Because after si meaning if, French normally does not use the future tense.

So French says:

• Si + present, then a present, future, or imperative idea in the other clause

Here, partons is the present tense of partir:

• Si nous partons trop tard... = If we leave too late...

Using si nous partirons would be incorrect in standard French.

A useful rule to remember is:

• si + present
• not si + future

Nous risquons de manquer le train literally means we risk missing the train.

French often uses the present tense here to express a real and immediate consequence. It sounds very natural.

So the sentence means something like:

• If we leave too late, we run the risk of missing the train.

You might hear or imagine nous risquerons de manquer le train, but nous risquons is the more natural choice in this kind of warning or statement about a likely consequence.

So:

• nous risquons = natural, common
• nous risquerons = grammatically possible in some contexts, but less idiomatic here

Risquer de + infinitive is a common French structure meaning:

• to risk doing something
• to be in danger of doing something
• to be likely to do something unpleasant

So:

• nous risquons de manquer le train = we risk missing the train

The de is simply part of the construction:

• risquer de + infinitive

Other examples:

• Il risque de pleuvoir. = It may rain / It risks raining.
• Tu risques de tomber. = You might fall.

So you should learn risquer de as a fixed pattern.

Because manquer can mean different things depending on how it is used.

In this sentence, manquer means to miss in the sense of fail to catch:

• manquer le train = to miss the train
• manquer l’avion = to miss the plane

Here, le train is a direct object, so there is no preposition.

But compare:

• manquer de temps = to lack time
• manquer d’argent = to lack money

That is a different meaning: to lack, which uses de.

So:

• manquer le train = miss the train
• manquer de temps = lack time

Trop tard means too late.

It is made up of:

• trop = too / excessively
• tard = late

So:

• partir trop tard = to leave too late

French usually places this kind of adverbial expression after the verb, so:

• nous partons trop tard

That word order is normal and natural.

Because French normally repeats the subject pronoun in each clause.

So French says:

• Si nous partons trop tard, nous risquons...

Even though English can sometimes avoid repetition more easily, French usually cannot.

You need a subject for both verbs:

• nous partons
• nous risquons

Leaving out the second nous would be ungrammatical.

Le train means the train, which suggests a specific train is meant — usually the one we are planning to take.

In context, that is the most natural choice:

• If we leave too late, we risk missing the train.

French often uses the definite article when the thing is already understood from the situation.

If you said un train, it would sound more like a train, any train, which is less likely here.

Partons is the 1st person plural present tense of partir.

The verb partir means to leave.

Its present tense is:

• je pars
• tu pars
• il/elle/on part
• nous partons
• vous partez
• ils/elles partent

So nous partons means we leave or we are leaving, depending on context.

Yes, essentially.

This sentence follows the common French pattern for a real or likely condition:

• Si + present, + result clause

Here:

• Si nous partons trop tard = if we leave too late
• nous risquons de manquer le train = we risk missing the train

This is the kind of structure English learners often think of as the first conditional, even though French tense usage is not always described in exactly the same way as English grammar.

The important practical rule is:

• For a real possible condition in French, use si + present

Yes, absolutely.

In everyday spoken French, on often replaces nous.

So:

• Si on part trop tard, on risque de manquer le train.

This sounds very natural in conversation.

The original version with nous is still completely correct, and it may sound a bit more careful, formal, or written.

So both are good:

• nous = more formal / more traditional
• on = very common in everyday speech

Here it means to miss in the sense of not catch in time.

So:

• manquer le train = to miss the train

Be careful, because manquer can be tricky in other contexts.

For example:

• Tu me manques literally means You are missing to me, which in natural English is I miss you.

So with people, the structure can feel reversed to an English speaker.

But in this sentence, it is the simple direct-object use:

• manquer le train = miss the train

No reversal here.

A careful pronunciation would be roughly:

• Si nous partons trop tard, nous risquons de manquer le train.
• see noo par-tohn troh tar, noo ree-skohn duh mahn-kay luh trahn

A few useful notes:

• The s in nous is normally silent.
• partons has a nasal sound in -ons.
• risquons also ends in a nasal sound.
• manquer ends with -ké, like kay.
• train has a nasal vowel, not a full n sound.

In normal speech, it may sound smoother and more connected than the spelling suggests.