Je vais acheter ces chaussures parce qu'elles sont en promotion.

Je vais acheter is the near future in French: aller + infinitive.

• je vais acheter = I am going to buy
• j'achèterai = I will buy

Both can refer to the future, but je vais acheter is very common in everyday spoken French and often suggests something planned or likely to happen soon.

In this sentence, it sounds natural because the speaker has basically decided to buy the shoes.

Because vais is the je form of the verb aller in the present tense.

The present tense of aller begins like this:

• je vais
• tu vas
• il/elle va
• nous allons
• vous allez
• ils/elles vont

So je vais acheter literally follows the pattern I go to buy, but in modern French it functions as I am going to buy.

In the structure aller + infinitive, only aller is conjugated. The second verb stays in the infinitive.

So:

• je vais acheter
• tu vas acheter
• nous allons acheter

not:

• je vais achète
• je vais achèterai

This is the standard pattern for the near future in French.

Ces is the plural demonstrative adjective, meaning these or those, depending on context.

French demonstratives are:

• ce for masculine singular
• cet for masculine singular before a vowel sound
• cette for feminine singular
• ces for plural

Since chaussures is plural, French uses ces.

So:

• cette chaussure = this shoe
• ces chaussures = these shoes

The singular noun is une chaussure, so it is feminine.

That matters because gender affects other words in French, especially in the singular:

• cette chaussure
• la chaussure

In the plural here, you still need to know the noun is feminine because later the pronoun becomes elles:

• chaussures → feminine plural
• therefore elles

Because que contracts before a vowel sound.

When que comes before elle, elles, il, ils, and many other vowel-starting words, it becomes qu':

• que elles → qu'elles
• que il → qu'il

This is very common in French and helps pronunciation flow more smoothly.

Elles refers back to ces chaussures.

Since chaussures is:

• plural
• feminine

the matching subject pronoun is elles.

Compare:

• Le livre est intéressant parce qu'il est court.
• Les chaussures sont en promotion parce qu'elles sont neuves.

If the noun were masculine plural, French would use ils instead.

Sont is the third-person plural form of être.

Because the subject is elles = they, the verb must also be plural:

• elle est
• elles sont

So:

• qu'elle est = because it/she is
• qu'elles sont = because they are

Here elles refers to the shoes, so sont is required.

The full expression is parce que, which means because.

But before a vowel sound, que becomes qu', so:

• parce que elles sont... becomes parce qu'elles sont...

This is just the normal contraction. You will see the same thing in many French sentences.

Both can mean because, but they are used a little differently.

• parce que is the most common and natural in everyday speech
• car is often more formal or written

So in a sentence like this, parce que is the most natural choice.

En promotion is a fixed expression meaning something like on sale or being sold at a reduced price.

It does not translate word-for-word in the same way English does. French often uses en in set expressions like this.

Examples:

• Ce téléphone est en promotion.
• Ces chaussures sont en promotion.

Learners often want to say something like sur promotion, but that is not idiomatic French here.

Sometimes, yes, but they are not always exactly the same.

• en promotion = on promotion / on sale in a broad sense
• soldé(e)(s) = marked down, usually during official sales periods

So ces chaussures sont en promotion is a very safe, common phrase. Ces chaussures sont soldées can also work in the right context, but it is a bit more specific.

French does not need an extra that in the same way English sometimes does. The structure is simply:

• parce que
  • clause

So:

• parce qu'elles sont en promotion

That whole part is just the clause introduced by because.

English and French do not always match word for word in these connectors.

A more formal version could use the simple future:

• J'achèterai ces chaussures parce qu'elles sont en promotion.

This is grammatically correct and natural, especially in writing. But in everyday spoken French, Je vais acheter... is extremely common and often more conversational.