Si vous choisissez celui-ci aujourd’hui, la remise s’applique aussi aux sandales et au gilet.

Si means if here. It introduces a condition:

• Si vous choisissez celui-ci aujourd’hui = If you choose this one today

This is a very common French pattern for real or likely conditions:

• Si + present, then present / future / imperative depending on the meaning.

In this sentence, both parts use the present tense because it describes a general rule or offer:

• If you choose this one today, the discount also applies...

Because after si meaning if, French normally uses the indicative, not the subjunctive.

So:

• si vous choisissez = if you choose

The form choisissiez is an imperfect subjunctive form and would not be used here in normal modern French.

Also, choisissez is the present tense form for vous of the verb choisir:

• je choisis
• tu choisis
• il/elle choisit
• nous choisissons
• vous choisissez
• ils/elles choisissent

Celui-ci means this one.

It is a demonstrative pronoun, used when you want to point to a masculine singular noun without repeating the noun itself.

For example, if people are looking at several jackets or products:

• celui-ci = this one
• celui-là = that one

It replaces a masculine singular noun, such as:

• le modèle → celui-ci
• le gilet → celui-ci
• le produit → celui-ci

French writes -ci and -là with a hyphen when they are attached to demonstrative pronouns or nouns.

Examples:

• celui-ci = this one
• celui-là = that one
• ce livre-ci = this book
• ce livre-là = that book

The -ci part suggests closeness, while -là suggests distance.

Because ce cannot stand alone before a pause in this kind of sentence, and ça is less precise.

• ce usually comes before a noun:
  
  • ce gilet = this cardigan
• celui-ci replaces the noun entirely:
  
  • celui-ci = this one

Ça can mean that/it, but it is more general and less specific. In a sentence about choosing one item among several, celui-ci is the natural choice.

Because historically it comes from au jour de hui, meaning something like on this day. In modern French, it is a fixed word meaning today.

You do not need to analyze it piece by piece in normal use; just learn:

• aujourd’hui = today

The apostrophe is simply part of the standard spelling.

La remise here means the discount.

In commercial contexts, French can use several words:

• une remise = a discount, often in sales or pricing contexts
• une réduction = a reduction/discount, also very common
• un rabais = discount/markdown, sometimes more direct or promotional

So la remise is a natural business or retail word here.

The verb here is s’appliquer à, which means to apply to.

So:

• la remise s’applique aux sandales et au gilet
  = the discount applies to the sandals and the cardigan

This is a very common French expression:

• Cette règle s’applique à tout le monde.
• L’offre s’applique seulement ce week-end.

French often uses the pronominal form s’appliquer where English simply says apply.

Because these are contractions of à + les and à + le.

French contracts them like this:

• à + le = au
• à + les = aux

So:

• à les sandales → aux sandales
• à le gilet → au gilet

This happens automatically in standard French.

Because sandales is plural and gilet is masculine singular.

• les sandales → with à becomes aux sandales
• le gilet → with à becomes au gilet

If it were feminine singular, there would be no contraction with la:

• à la veste

So the forms depend on the article:

• au = to the / applies to the masculine singular noun
• à la = to the feminine singular noun
• aux = to the plural noun

Aussi means also. Here it modifies the idea that the discount applies not only to one thing, but to these items as well.

• la remise s’applique aussi aux sandales et au gilet

This placement is natural in French. It comes before the phrase being added.

In English, also can move around a bit more. In French, word order is usually less flexible, so aussi is often placed exactly like this.

It could be either.

In French, vous can mean:

• you when speaking to more than one person
• you as the polite singular form

In a sales or customer-service sentence like this, it is very likely the polite singular or a polite general address to the customer.

French uses articles more often than English, especially with nouns in general statements.

So French naturally says:

• aux sandales et au gilet

Even though English might say:

• to sandals and the cardigan or more naturally:
• to the sandals and the cardigan

In French, leaving out the articles here would sound wrong.

Sometimes French uses sur with discounts, but not in the same structure.

Compare:

• une remise sur les sandales = a discount on the sandals
• la remise s’applique aux sandales = the discount applies to the sandals

So both ideas exist, but the verb pattern changes:

• remise sur + noun
• s’appliquer à + noun

In this sentence, because the verb is s’applique, à is the correct preposition.

Choisissez is the vous form of choisir in the present tense.

The -ez ending is the normal present-tense ending for many verbs with vous:

• vous parlez
• vous finissez
• vous choisissez

It is pronounced roughly like shwa-zee-say.

So:

• vous choisissez = you choose

It sounds neutral to polite, which fits a shop, advertisement, or customer-service setting.

Reasons:

• vous is polite or formal
• la remise sounds like retail/business language
• the whole sentence is clear and standard, not casual slang

A more casual version might use tu if speaking to a friend, but that would change the verb:

• Si tu choisis celui-ci aujourd’hui...