Je pose une serviette froide sur mon front quand j’ai de la fièvre.

Yes, je mets would also be possible in many situations.

• poser means to place, to set down
• mettre means to put

In this sentence, poser suggests carefully placing the towel on the forehead. Mettre is more general and very common in everyday speech.

So:

• Je pose une serviette froide sur mon front = I place a cold towel on my forehead
• Je mets une serviette froide sur mon front = I put a cold towel on my forehead

Both are natural, but poser can sound a little more deliberate.

Because serviette is a feminine singular noun, so both the article and the adjective must match it.

• serviette = feminine singular
• une = feminine singular form of a
• froide = feminine singular form of cold

Compare:

• un tissu froid = a cold cloth
• une serviette froide = a cold towel

The adjective changes form to agree with the noun.

In French, most adjectives come after the noun.

So:

• une serviette froide = a cold towel
• une soupe chaude = a hot soup
• un jour important = an important day

A small group of common adjectives often comes before the noun, but froid / froide normally comes after it.

That is a very common question. Serviette can mean different things depending on context.

It often means:

• napkin
• towel
• sometimes small towel or washcloth, depending on the situation

In this sentence, because it is cold and placed on the forehead during a fever, the meaning is clearly something like a towel or a cold cloth, not a dinner napkin.

Context tells you which meaning is intended.

Both patterns exist in French, but mon front is very natural here.

French often uses the definite article with body parts, especially when a reflexive verb is involved:

• Je me lave les mains = I wash my hands
• literally: I wash the hands to myself

But here the verb is not reflexive, and the speaker is simply saying where the towel is placed, so sur mon front is perfectly normal and clear.

So:

• sur mon front = on my forehead

This is a good, standard way to say it.

Because French shortens je before a vowel sound.

• je ai is not used
• it becomes j’ai

This is called elision.

You will see this a lot:

• j’ai = I have
• j’aime = I like / I love
• j’habite = I live
• j’écoute = I listen

So je becomes j’ before a vowel or a silent h.

In French, the normal expression is avoir de la fièvre, literally to have fever.

This is just the standard idiom. Languages do not always package ideas the same way.

• J’ai de la fièvre = I have a fever / I have fever
• Il a de la fièvre = He has a fever

The important thing is to learn it as a set expression: avoir de la fièvre.

Here de la is part of the usual expression avoir de la fièvre.

French often uses a partitive article with things seen as an amount, condition, or substance:

• avoir de la chance = to be lucky
• avoir du courage = to have courage
• avoir de la fièvre = to have a fever

Using la fièvre would usually sound more specific, as if talking about the fever in a particular context, not just the condition in general.

So in a basic statement like this, de la fièvre is the normal choice.

Because French uses the present tense for general habits and repeated actions, just like English often does.

This sentence describes what the speaker does whenever that situation happens:

• Je pose une serviette froide sur mon front quand j’ai de la fièvre.

It means something like:

• I put a cold towel on my forehead when I have a fever
• Whenever I have a fever, I put a cold towel on my forehead

So this is not only about one specific moment right now. It can describe a usual practice.

Yes, lorsque is possible, but quand is more common and more natural in everyday speech.

• quand = when
• lorsque = when, but slightly more formal or literary in many contexts

So:

• Je pose une serviette froide sur mon front quand j’ai de la fièvre. = very natural everyday French
• ... lorsque j’ai de la fièvre. = also correct, but a little more formal

Front is pronounced roughly like fron with a nasal vowel.

A few helpful points:

• the t at the end is normally silent
• the on is nasal, so it does not sound like English on
• it is one syllable

So front does not sound like the English word front.

In the whole phrase:

• sur mon front

the final r in sur is pronounced, mon has a nasal vowel, and front also has a nasal vowel.

Yes. This part can be tricky for learners.

• quand ends with a nasal sound
• j’ai begins with the sound zh as in the middle of measure, followed by é

So quand j’ai flows together smoothly. In careful speech, the d of quand is usually not strongly pronounced here.

A rough guide is:

• quand j’ai ≈ kan zhé

That is only an approximation, but it helps show the rhythm.

In some varieties of French, yes, but j’ai de la fièvre is the standard and widely understood expression.

A learner should definitely know and use:

• avoir de la fièvre

because it is the most reliable and common way to express this idea.