Le chat dort, et le chien marche autour de lui.

In French, singular countable nouns usually need an article. So you normally say:

• le chat = the cat
• le chien = the dog

Unlike English, French usually does not say just cat sleeps or dog walks. You generally need le, la, un, une, etc.

Dort is the 3rd person singular present tense form of the verb dormir.

The verb is conjugated like this in the present:

• je dors
• tu dors
• il/elle/on dort
• nous dormons
• vous dormez
• ils/elles dorment

Since le chat is equivalent to it or he, French uses the il/elle form, so:

• Le chat dort = The cat sleeps / is sleeping

It can mean both, depending on context.

In French, the simple present often covers both:

• walks
• is walking

So:

• Le chien marche can mean The dog walks or The dog is walking

In this sentence, because of the situation being described, English would most naturally say is walking around him, but French simply uses the present tense.

Because autour de is a fixed expression in French.

You must say:

• autour de quelqu’un = around someone
• autour de quelque chose = around something

So:

• autour du chat = around the cat
• autour de lui = around him

You cannot drop de here.

After a preposition such as de, French uses a stressed pronoun.

The stressed pronouns include:

• moi
• toi
• lui
• elle
• nous
• vous
• eux
• elles

Since de is a preposition, French says:

• de lui = of him / from him
• autour de lui = around him

You would not use a direct object pronoun like le here.

Here, lui refers to le chat.

So the sentence means that:

• the cat is sleeping
• the dog is walking around the cat

Because chat is masculine, the pronoun used is lui.

Yes, absolutely.

Both are correct:

• Le chat dort, et le chien marche autour du chat.
• Le chat dort, et le chien marche autour de lui.

Using de lui avoids repeating le chat, so it sounds more natural in many contexts.

The comma is acceptable because the sentence joins two full clauses:

• Le chat dort
• le chien marche autour de lui

French punctuation is often a bit flexible here, just as in English. You could also write:

• Le chat dort et le chien marche autour de lui.

So the comma is not required, but it is not wrong.

Yes. This sentence follows a very familiar pattern:

• Le chat = subject
• dort = verb

and

• le chien = subject
• marche = verb
• autour de lui = prepositional phrase

So the structure is very close to English:

• The cat sleeps, and the dog walks around him.

That makes this sentence relatively straightforward for English speakers.

In French, chat and chien are grammatically masculine nouns, which is why they use le.

That does not automatically mean the animals are biologically male. Grammatical gender and real-life sex are not always the same thing in everyday sentences.

So:

• le chat = the cat
• le chien = the dog

Here, lui is masculine because chat is grammatically masculine in the sentence.

Yes, this word can be tricky for English speakers.

A rough guide:

• chat sounds like sha
• chien sounds roughly like shyen
• dort sounds roughly like dor
• marche sounds roughly like marsh
• lui sounds roughly like lwee

A couple of important points:

• final consonants are often silent, so the t in chat and dort is not pronounced
• ch in French usually sounds like sh, not like English ch in chair

It could be, but then the meaning might become less clear unless the context already tells you who il is.

Compare:

• Le chat dort, et le chien marche autour de lui.
• Le chat dort, et il marche autour de lui.

In the second version, il could be confusing, because it might seem to refer to the cat or the dog.

By repeating le chien, the sentence stays clear and easy to understand.

Sometimes, yes, depending on context.

• Le chat dort literally means The cat sleeps or The cat is sleeping
• In natural English, if you are describing a current situation, The cat is asleep may also fit

But grammatically, dort comes from the verb dormir = to sleep, so the most direct translation is still based on sleep.