Je reprends la serpillière parce qu’il y a encore de la mousse sur le sol.

Reprendre means to take again, to pick up again, or to resume using something. In this sentence, Je reprends la serpillière suggests I’m using the mop again because the floor still isn’t clean enough.

If you said Je prends la serpillière, that would simply mean I take the mop.
With reprends, the idea is that the speaker had already used it before and is now going back to it.

In French, you usually need an article before a noun. So serpillière normally appears as la serpillière.

French uses articles much more often than English does. Where English might say I’m grabbing the mop, French naturally says Je prends la serpillière.

Also, serpillière is a feminine singular noun, so the article is la.

Une serpillière is a mop or sometimes a floor cloth, depending on context and region.

In this sentence, the natural English meaning is mop, because the speaker is cleaning the floor and there is still foam left on it.

So:

• la serpillière = the mop

This is because of elision. When que is followed by a word beginning with a vowel sound, the e drops and becomes an apostrophe:

• parce que il → parce qu’il

This is very common in French:

• que elle → qu’elle
• que on → qu’on
• je aime → j’aime

So parce qu’il is just the normal contracted form.

Il y a means there is or there are.

So:

• il y a encore de la mousse sur le sol = there is still some foam on the floor

French uses il y a as the normal way to express existence:

• Il y a un problème = There is a problem
• Il y a des gens dehors = There are people outside

Even though il literally looks like he, in il y a it does not refer to a person.

De la is a partitive article. It is used when talking about an unspecified amount of something that is not being counted.

Here, mousse means foam or suds, and the sentence means there is some foam left on the floor.

So:

• de la mousse = some foam

French often uses partitive articles where English may use nothing or some:

• Je bois de l’eau = I drink water / I drink some water
• Il y a du savon = There is some soap

Because mousse is feminine singular, the partitive form is de la.

Here, encore means still.

So:

• il y a encore de la mousse = there is still some foam

Depending on context, encore can also mean again:

• Dis-le encore = Say it again

But in this sentence, the meaning is clearly still, because it describes a situation that continues.

In this sentence, encore modifies the idea expressed by il y a — in other words, it tells you that the foam is still there.

So French says:

• il y a encore de la mousse

This is the natural word order for there is still...

English and French do not always place adverbs in the same position, so it is best to learn il y a encore... as a common pattern.

Sur le sol means on the floor.

• sur = on
• le sol = the floor / the ground

Sol is a slightly more neutral or formal word for floor/surface underfoot. In everyday speech, people may also say par terre in some contexts, but sur le sol is very natural when talking about cleaning.

So:

• sur le sol = on the floor

Sometimes yes, but the meaning and tone are a little different.

• sur le sol focuses on the physical surface of the floor
• par terre often means on the ground or on the floor, especially in the sense of location

In a cleaning sentence, sur le sol sounds very natural because you are talking about foam remaining on the floor surface. Par terre might also be understood, but sur le sol fits especially well here.

Reprends is pronounced approximately like ruh-pran.

A few helpful points:

• the re- is not like English ree; it is more like a weak French ruh
• prends has a nasal vowel, so the en is not pronounced like a full English en
• the final -ds is usually silent

So the whole beginning:

• Je reprends ≈ zhuh ruh-pran

Serpillière is pronounced approximately sehr-pee-yehr.

A few details:

• ser sounds roughly like sehr
• pill sounds like pee
• ière sounds like yehr
• the stress in French is much flatter than in English, so don’t stress one syllable too strongly

A rough guide:

• la serpillière ≈ la sehr-pee-yehr

Yes. The sentence is in the present tense.

• Je reprends = I take again / I pick up again / I’m taking up again
• il y a = there is
• il y a encore = there is still

French present tense can often translate into English in more than one way depending on context:

• Je reprends la serpillière could be I take the mop again, I pick the mop back up, or I’m using the mop again

French uses il y a to say that something exists or is present somewhere.

So:

• il y a de la mousse = there is some foam

You would not use il est here, because être is not the normal structure for there is/there are in French.

Think of it this way:

• il y a = there is / there are
• il est = he is / it is in other kinds of sentences

The sentence breaks down like this:

• Je reprends la serpillière = main clause
• parce qu’ = because
• il y a encore de la mousse sur le sol = reason

So the full structure is:

[main action] + parce que + [reason]

That is a very common French pattern:

• Je ferme la fenêtre parce qu’il fait froid.
• Je recommence parce qu’il y a encore une erreur.

In your sentence, the speaker explains why they are taking the mop again: because there is still foam on the floor.