Si ton bagage est trop lourd, je peux t’aider à le porter jusqu’au quai.

Si means if here.

So Si ton bagage est trop lourd... means If your luggage is too heavy...

A common point of confusion is that si can also mean yes when replying to a negative question or statement, but in this sentence it is clearly the if meaning.

Because bagage is a masculine singular noun in French.

• ton = your (for a masculine singular noun)
• ta = your (for a feminine singular noun)
• tes = your (for plural nouns)

So:

• ton bagage = your luggage
• not ta bagage

In French, bagage can work as a collective singular noun, much like luggage in English.

So ton bagage can mean:

• your luggage
• your bag
• your baggage

French can also use the plural bagages, but the singular is very natural when talking about someone’s luggage in a general sense.

Because the adjective has to agree with bagage, which is masculine singular.

• masculine singular: lourd
• feminine singular: lourde
• masculine plural: lourds
• feminine plural: lourdes

Since it is ton bagage, the correct form is lourd.

Trop lourd means too heavy.

• trop = too
• lourd = heavy

So:

• est trop lourd = is too heavy

French usually places trop before the adjective:

• trop lourd
• trop grand
• trop cher

Because in French, object pronouns like me, te, le, la, nous, vous, les normally go before the verb.

So:

• aider toi is not correct
• t’aider = help you

Here:

• t’ is the shortened form of te
• it becomes t’ before a vowel sound: t’aider

So:

• je peux t’aider = I can help you

This is a very common French pattern.

The apostrophe shows elision.

Te becomes t’ before a word starting with a vowel or silent h:

• te aider → t’aider
• te écouter → t’écouter
• te inviter → t’inviter

French does this to make pronunciation smoother.

Because aider often follows the pattern:

aider quelqu’un à faire quelque chose
= to help someone do something

So:

• je peux t’aider à porter... = I can help you carry...

In this sentence, the thing being carried is expressed with le, so we get:

• je peux t’aider à le porter
  = I can help you carry it

Le refers back to ton bagage.

Since bagage is masculine singular, the pronoun is le.

So instead of repeating ton bagage, French uses the pronoun:

• porter ton bagage = carry your luggage
• le porter = carry it

This avoids repetition, just like English does.

Because the speaker wants to say carry it, not just carry in a general sense.

Compare:

• t’aider à porter = help you carry
• t’aider à le porter = help you carry it

The le makes it clear that the object is the luggage already mentioned earlier.

Jusqu’au is a combination of:

• jusqu’à = up to / until / as far as
• le = the

Since à + le contracts to au, we get:

• jusqu’à le → jusqu’au

So:

• jusqu’au quai = as far as the platform / to the platform

This kind of contraction is very common in French:

• à + le = au
• à + les = aux
• de + le = du
• de + les = des

Here, quai most likely means platform, especially in a train-station context.

Depending on context, quai can also mean:

• a platform
• a dock
• a quay
• a riverside embankment

But in this sentence, jusqu’au quai would usually be understood as to the platform.

Because quai is masculine singular and takes le as its article:

• le quai

After à, le becomes au:

• à le quai → au quai

And after jusqu’à, that gives:

• jusqu’au quai

So the sentence uses the normal contraction rule.

Yes. Porter has several meanings in French, including:

• to carry
• to wear
• sometimes to bear or to bring

In this sentence, because the object is bagage, the meaning is clearly to carry:

• porter un bagage = to carry luggage

If it were clothes, porter could mean to wear:

• porter une veste = to wear a jacket

A very natural English rendering would be:

• If your luggage is too heavy, I can help you carry it to the platform.

French and English are very close here, but French often keeps a slightly more explicit structure:

• t’aider à le porter = help you to carry it
• jusqu’au quai = as far as the platform / to the platform

So the French sentence is structurally very straightforward once you break it into parts.