Au camping, je garde la boussole dans mon sac.

Because au is the contracted form of à + le.

• à le camping → au camping

French usually contracts à + le into au. So au camping means something like at the campsite / at the campground.

This kind of contraction is very common:

• à + le parc → au parc
• à + le supermarché → au supermarché

But note:

• à + la stays à la
• à + l' stays à l'
• à + les becomes aux

Au camping usually means at the campsite / at the campground.

It refers to being in that location or setting. In context, it sounds natural to understand the sentence as something like:

• At the campsite, I keep the compass in my bag.

Depending on context, English might also express the idea as when camping, but the French here is more literally about location: at the campground/campsite.

The comma separates an introductory phrase from the rest of the sentence.

• Au camping sets the scene.
• Then the main clause follows: je garde la boussole dans mon sac.

English does the same thing very often:

• At the campsite, I keep the compass in my bag.

In French, the comma is helpful and natural here, especially because Au camping is a short phrase placed at the beginning for emphasis or context. Without the comma, the sentence would still often be understandable, but the comma makes the structure clearer.

Because je garde is the conjugated verb, while garder is the infinitive.

• garder = to keep
• je garde = I keep

French verbs have to be conjugated to match the subject:

• je garde = I keep
• tu gardes = you keep
• il/elle garde = he/she keeps
• nous gardons = we keep
• vous gardez = you keep
• ils/elles gardent = they keep

So after je, you need garde, not garder.

Not exactly. Garder often means to keep, to leave, to maintain, or to look after, depending on context.

Here, je garde la boussole dans mon sac means:

• I keep the compass in my bag.

It does not mean I guard the compass in the English sense of protecting it like a security guard.

Some examples of garder:

• Je garde mes clés dans ma poche. = I keep my keys in my pocket.
• Elle garde les enfants. = She looks after the children.
• Gardez le silence. = Keep quiet.

So here, think of garder as keep.

In French, nouns usually need an article or another determiner.

So instead of saying just boussole, French normally says:

• la boussole = the compass
• une boussole = a compass
• ma boussole = my compass

French uses articles more often than English does. Even when English might omit one in some contexts, French usually keeps one.

Here, la boussole refers to a specific compass, so the compass is natural.

La shows that boussole is a feminine singular noun.

In French, every noun has grammatical gender:

• le = masculine singular
• la = feminine singular
• les = plural

So:

• la boussole = the compass

The gender here is grammatical, not biological. A compass is not female in any real-world sense; boussole is simply a feminine noun in French.

This matters because adjectives and some other words may need to agree with it:

• la petite boussole = the small compass

Because French does not combine a possessive adjective like mon with a definite article like le in this kind of structure.

You say:

• mon sac = my bag

Not:

• le mon sac
• mon le sac

French chooses one determiner:

• le sac = the bag
• un sac = a bag
• mon sac = my bag

All three fill the same grammatical slot before the noun.

Dans means in / inside. It is the natural preposition when something is physically inside a container.

So:

• dans mon sac = in my bag

Some related prepositions:

• sur mon sac = on my bag
• sous mon sac = under my bag
• près de mon sac = near my bag

Since the compass is being kept inside the bag, dans is the correct choice.

This is the normal French word order:

• subject
  • verb
    • object
      • prepositional phrase

So here:

• je = subject
• garde = verb
• la boussole = direct object
• dans mon sac = where it is kept

That gives:

• Je garde la boussole dans mon sac.

This is very similar to standard English word order:

• I keep the compass in my bag.

Yes, absolutely.

• la boussole = the compass
• ma boussole = my compass

Both are grammatically correct, but they mean slightly different things.

• Je garde la boussole dans mon sac.
  This points to a specific compass already known from context.
• Je garde ma boussole dans mon sac.
  This emphasizes that it is my compass.

French often chooses between the and my based on context, just like English.

Yes. Camping exists in French, borrowed from English, but its usage is a little different.

In French, un camping usually means:

• a campsite
• a campground
• a camping site/business

So au camping means at the campsite/campground, not necessarily the activity of camping in the abstract.

That is why a learner should be careful not to assume French camping always works exactly like English camping.

A simple pronunciation guide is:

• Au camping, je garde la boussole dans mon sac.
• roughly: oh kahm-peeng, zhuh gard lah boo-sohl dahn mohn sahk

A few useful points:

• Au sounds like oh.
• je begins with the soft zh sound, like the s in measure.
• garde has a hard g sound.
• boussole sounds roughly like boo-sohl.
• dans has a nasal vowel; the n is not fully pronounced like English n.
• mon also has a nasal vowel.
• The final c in sac is pronounced.

This is only an approximation, but it can help at the beginning.