Je remets toujours mes clés dans mon sac pour ne pas les perdre.

Because remettre and mettre are related but not identical.

• mettre = to put
• remettre = to put back, put again, return, hand back

So:

• Je mets mes clés dans mon sac = I put my keys in my bag
• Je remets mes clés dans mon sac = I put my keys back in my bag

In this sentence, remets suggests a habitual action of returning the keys to their usual place.

The prefix re- often means again or back in French, just like re- in English words such as return or replace.

So:

• mettre = to put
• remettre = to put back / put again

This is very common in French. For example:

• faire = to do

• refaire = to do again

• venir = to come
• revenir = to come back

It is the present tense: je remets = I put back / I am putting back / I do put back, depending on context.

Here, because of toujours and the overall meaning, it is best understood as a habitual present:

• Je remets toujours mes clés... = I always put my keys back...

So it describes something the speaker regularly does.

In French, short adverbs like toujours, souvent, déjà, and bien often come after the conjugated verb.

So:

• Je remets toujours mes clés...

This is the normal word order.

Compare:

• Je mange souvent ici. = I often eat here.
• Il est déjà parti. = He has already left.

English often puts adverbs in different places, so this can feel unusual at first.

Mes clés means my keys. French often uses a possessive adjective when talking about personal belongings.

• mes = my
• clés = keys

So mes clés is the natural way to say my keys.

You could say les clés if the context already made it completely obvious which keys you meant, but mes clés is more normal here.

Because sac is a masculine noun in French.

So:

• mon sac = my bag
• ma table = my table

French possessive adjectives agree with the gender and number of the noun possessed, not with the gender of the owner.

So even if the speaker is female, she still says:

• mon sac
• mes clés

Clés is plural because the speaker has more than one key.

And mes is the plural form of my.

Compare:

• ma clé = my key
• mes clés = my keys

So mes is used with plural nouns, whether those nouns are masculine or feminine.

Examples:

• mes amis = my friends
• mes chaussures = my shoes
• mes clés = my keys

Dans means in or inside.

So:

• dans mon sac = in my bag

It shows physical location: the keys go inside the bag.

French uses dans very naturally for something placed inside a container:

• dans la boîte = in the box
• dans la poche = in the pocket
• dans le tiroir = in the drawer

Here pour means in order to or so as to when followed by an infinitive.

So:

• pour ne pas les perdre = so as not to lose them

This is a very common French structure:

• Je viens pour aider. = I’m coming to help.
• Elle écrit pour expliquer. = She writes to explain.

In this sentence, pour introduces the purpose of putting the keys back in the bag.

Because in French, with an infinitive, the negation is usually:

• ne pas + infinitive

So:

• ne pas perdre = not to lose

If there is an object pronoun like les, it goes right before the infinitive:

• ne pas les perdre = not to lose them

So the correct order is:

• pour ne pas les perdre

Not:

• pour ne les pas perdre

That order sounds wrong in modern French.

Les is the direct object pronoun meaning them, and it refers back to mes clés.

So instead of repeating mes clés, French uses the pronoun:

• pour ne pas perdre mes clés
• pour ne pas les perdre

Both are possible, but the second one is more natural because it avoids repetition.

Since clés is plural, the pronoun is les.

In French, object pronouns usually come before the verb they belong to.

Here, the verb is the infinitive perdre, so the pronoun comes before it:

• les perdre = to lose them

This is the normal pattern with infinitives:

• Je vais les prendre. = I’m going to take them.
• Il préfère les garder. = He prefers to keep them.
• pour ne pas les perdre = so as not to lose them

This is different from English, where the pronoun usually comes after the verb: lose them.

Yes. That is also correct.

• pour ne pas perdre mes clés = so as not to lose my keys
• pour ne pas les perdre = so as not to lose them

The version with les is just smoother because it avoids repeating mes clés.

French often prefers the pronoun once the noun has already been mentioned.

Yes, the meaning is essentially the same.

• pour ne pas les perdre = so as not to lose them
• afin de ne pas les perdre = in order not to lose them

But afin de is usually a bit more formal or more deliberate in tone.
In everyday speech, pour is more common and more natural.

A simple pronunciation guide is:

zhuh ruh-MEH too-ZHOOR may clay dahn mohn sak poor nuh pah lay pair-dr

A few useful points:

• je sounds like zhuh
• remets sounds like ruh-MEH
  The final -ts is not pronounced.
• toujours sounds roughly like too-ZHOOR
• clés sounds like clay
• dans has a nasal vowel, so it is not pronounced like English dan
• mon also has a nasal vowel
• les perdre: the r sound is French, produced in the back of the throat

You may also hear natural linking and smoothing in fast speech, but word by word this is a good start.

You can see both clé and clef.

They mean the same thing:

• une clé
• une clef

Today, clé is very common and often preferred in modern spelling, but clef is still also correct.

So mes clés could also be written mes clefs.

Not usually. In normal context, Je remets toujours mes clés dans mon sac means a habit:

• I always put my keys back in my bag

If you wanted to emphasize repeated action in an ongoing situation, French would usually use a different structure or more context.

So the basic reading here is: this is something the speaker regularly does to avoid losing the keys.

Word by word, it is roughly:

• Je = I
• remets = put back
• toujours = always
• mes clés = my keys
• dans mon sac = in my bag
• pour = in order to / so as to
• ne pas = not
• les = them
• perdre = lose

So the structure is:

I put back always my keys in my bag in order not them to lose

That is not good English, of course, but it helps show how the French pieces fit together. The natural English version is:

I always put my keys back in my bag so I don’t lose them.