Je prépare une soupe maison quand il fait froid.

Because this sentence expresses a habit or something that is generally true: whenever it is cold, I make homemade soup.

In French, the present tense is often used for habitual actions, just like in English:

• Je prépare une soupe maison quand il fait froid.
• I make homemade soup when it’s cold.

If you wanted to talk about right now, context would usually make that clear, or you could say something more specific.

It can mean either one, depending on context.

French uses the simple present much more broadly than English does. So:

• Je prépare can mean I prepare / I make
• and sometimes I am preparing

In this sentence, because of quand il fait froid, the natural interpretation is habitual: I make homemade soup when it’s cold.

Une soupe means a soup or one soup, so it presents the soup as a specific dish or serving.

De la soupe is more like some soup or soup as an uncountable food.

So both are possible, but the nuance is different:

• Je prépare une soupe maison quand il fait froid.
  = I make a homemade soup / a homemade soup dish when it’s cold.

• Je prépare de la soupe maison quand il fait froid.
  = I make homemade soup when it’s cold.

The version with de la soupe may sound a little more natural in everyday speech if you are talking about soup in general, but une soupe maison is still perfectly understandable.

Here, maison means homemade.

So:

• une soupe maison = a homemade soup

This is a very common use in French for food:

• des frites maison = homemade fries
• un dessert maison = a homemade dessert

It comes from the idea of something being from the house or house-made.

Because in this use, maison is usually treated as an invariable expression after the noun, especially in food language.

So you say:

• une soupe maison
• des soupes maison

Not:

• une soupe maisonne or anything like that

If you want a more fully adjectival expression, French often uses:

• fait maison / faite maison

For example:

• une soupe faite maison = a homemade soup

Since soupe is feminine singular, faite agrees with it.

French usually uses il fait + weather expression for talking about weather or temperature.

So:

• il fait froid = it is cold
• il fait chaud = it is hot
• il fait beau = the weather is nice
• il fait mauvais = the weather is bad

C’est froid usually means that something is cold:

• La soupe, c’est froid. = The soup is cold.

So for general weather, il fait froid is the normal expression.

It does not refer to a real person or thing. It is an impersonal subject, like it in English weather expressions.

So in:

• il fait froid

the il is just required by French grammar. It does not mean he here.

The same thing happens in:

• il pleut = it’s raining
• il neige = it’s snowing
• il faut partir = it is necessary to leave

Quand means when. In this sentence, it introduces the situation in which the action usually happens:

• Je prépare une soupe maison quand il fait froid.
• I make homemade soup when it’s cold.

It works well for repeated situations and general habits.

You could also sometimes use lorsqu’ in more formal French:

• Je prépare une soupe maison lorsqu’il fait froid.

But quand is very common and natural in everyday speech.

Because both parts describe something general or habitual:

• Je prépare = I make / I prepare
• il fait froid = it is cold

French often uses the present tense in both clauses for this kind of statement:

• Je lis quand j’ai le temps. = I read when I have time.
• Nous sortons quand il fait beau. = We go out when the weather is nice.

If you were talking about the future, the tenses would normally change:

• Je préparerai une soupe maison quand il fera froid.
• I’ll make homemade soup when it gets cold.

Yes, you could, and it would sound natural.

The difference is small:

• préparer focuses on preparing
• faire is a very common general verb meaning to make

So:

• Je prépare une soupe maison = I prepare a homemade soup
• Je fais une soupe maison = I make a homemade soup

In many everyday situations, faire may sound a bit more conversational, while préparer can sound slightly more deliberate or descriptive.

The word order is very standard:

• Je = subject
• prépare = verb
• une soupe maison = object
• quand il fait froid = time/condition clause

So the structure is: subject + verb + object + subordinate clause

French word order is often less flexible than English, so this straightforward order is a good model to follow.

Not normally. As written, it most naturally means a habit or general tendency.

If you want a clear future meaning, French usually changes both verbs to the future:

• Je préparerai une soupe maison quand il fera froid.

That means:

• I’ll make homemade soup when it’s cold / when it gets cold.

So the original sentence is best understood as a present-time general statement, not a future promise.