Sur le sable, nous trouvons souvent un coquillage cassé ou un petit morceau de verre.

Sur le sable means on the sand. French often puts a place expression at the beginning of the sentence to set the scene.

So:

• Sur le sable, nous trouvons souvent...
• literally: On the sand, we often find...

This is similar to English sentences like:

• On the beach, we often find...
• In winter, people wear coats.

The comma helps separate that introductory location phrase from the rest of the sentence.

Both can exist, but they suggest different things.

• sur le sable = on the sand, on the surface
• dans le sable = in the sand, inside or buried in the sand

In this sentence, the idea is that while walking along the beach, you often find things on the sand, so sur is the natural choice.

Yes. Both are possible, but they feel a little different.

• nous trouvons = we find
• on trouve = literally one finds, but in everyday French it very often means we find

In modern spoken French, on trouve souvent... is more common in casual conversation.
Nous trouvons souvent... sounds a bit more formal, careful, or written.

So this sentence is perfectly correct, but in everyday speech many people would say:

• Sur le sable, on trouve souvent un coquillage cassé...

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

So:

• nous trouvons souvent
• not usually nous souvent trouvons

This is a very common French word order pattern:

• Je mange souvent ici.
• Il parle toujours vite.
• Nous allons déjà partir.

So nous trouvons souvent is the normal placement.

Because cassé is an adjective, and in French many adjectives come after the noun.

Here:

• coquillage = shell / seashell
• cassé = broken

So:

• un coquillage cassé = a broken shell

This is the normal position for many descriptive adjectives, especially ones describing condition, shape, color, or result:

• une porte fermée = a closed door
• un verre brisé = a shattered glass
• une fleur rouge = a red flower

French adjectives do not all go in the same place.

Some adjectives usually come before the noun, especially common short ones about:

• size
• age
• beauty
• goodness

That is why we get:

• un petit morceau = a small piece

But many other adjectives usually come after the noun, including adjectives like cassé:

• un coquillage cassé = a broken shell

So the sentence shows both common patterns:

• petit before the noun
• cassé after the noun

After expressions of quantity or pieces, French usually uses de without a definite article.

So:

• un morceau de verre = a piece of glass
• un morceau de pain = a piece of bread
• un verre d’eau = a glass of water

You would use du only if you meant something more specific like a piece of the glass in a very particular context. But here the meaning is simply a small piece made of glass or a shard of glass, so de verre is correct.

This is a very useful vocabulary question.

• coquillage usually means a shell, especially a seashell, or sometimes shellfish depending on context
• coquille often means a shell too, but more in the sense of a shell as a covering, or in some fixed expressions

In a beach sentence like this, un coquillage is very natural for a seashell.

So if you are talking about something you find on the beach, coquillage is the safest choice.

Because French, like English, often uses the singular to talk about a typical example.

So:

• nous trouvons souvent un coquillage cassé
• literally: we often find a broken shell

This does not mean only one shell ever exists. It means that, on a typical occasion, what you find is a broken shell or a small piece of glass.

English does this too:

• You often see a bird in this garden.
• At the market, you can buy a good cheese.

The singular presents one representative item.

Not necessarily. Here ou simply introduces alternatives:

• un coquillage cassé
• ou
• un petit morceau de verre

It means that on the sand, you often find one kind of thing or the other. In real life, you could of course find both. The sentence is just listing common possibilities, not making a strict logical rule.

A careful pronunciation would be roughly:

Sur le sable, nous trouvons souvent un coquillage cassé ou un petit morceau de verre.

A few useful points:

• sur le sable: the r in sur is the French r
• nous trouvons: trouvons ends with a nasal sound in -ons
• souvent: many modern speakers do not pronounce the t
• un has the French nasal vowel, not an English un
• ou un may sound linked smoothly in speech
• petit: the final t is usually silent
• verre sounds like vair/vers/vert — these words sound the same in standard French

If you want a simple pronunciation guide for the whole sentence, an English speaker might approximate it as:

Sur luh sabl, noo troo-von soo-von un kuh-kee-yazh kah-say oo un puh-tee mor-so duh verr

That is only approximate, but it can help as a first step.

Yes, it could:

• Sur le sable nous trouvons souvent...

But the comma is very natural because Sur le sable is an introductory phrase. It helps readability and marks a small pause. In careful writing, many people would include it.

So:

• with comma = clearer, more natural in many contexts
• without comma = still understandable

Yes. Depending on context, un petit morceau de verre can be translated in slightly different ways:

• a small piece of glass
• a piece of glass
• a little shard of glass
• a small shard of glass

The French phrase itself is neutral and literal. English often chooses shard if the glass is broken and dangerous, which is probably the idea here.