הוא לא רוקד מהר, אבל הוא תמיד שמח לרקוד עם האחות שלו.

Because the sentence has two clauses:

• הוא לא רוקד מהר = he does not dance quickly
• אבל הוא תמיד שמח לרקוד עם האחות שלו = but he is always happy to dance with his sister

In Hebrew, it is very normal to repeat the subject pronoun in a new clause, especially after a word like אבל meaning but. Also, present-tense verb forms in Hebrew show gender and number, but not person clearly enough to always drop the pronoun, so הוא often stays.

לא means not.

In Hebrew, לא usually comes directly before the word or phrase it negates. Here it comes before the verb:

• הוא לא רוקד = he is not dancing / he does not dance

So לא works much more simply than English do/does not.

רוקד is the masculine singular present-tense form of לרקוד meaning to dance.

It matches the subject הוא = he.

A few matching examples:

• הוא רוקד = he dances
• היא רוקדת = she dances
• הם רוקדים = they dance
• הן רוקדות = they dance

So the form changes for gender and number.

Hebrew does not use do-support the way English does.

English says:

• He does not dance

Hebrew simply says:

• הוא לא רוקד

So there is no separate helper verb like do/does here. You just use לא plus the verb.

Here מהר means quickly or fast, so it is functioning as an adverb.

• רוקד מהר = dances quickly

In Hebrew, words like מהר do not change form to match gender or number in this use. So you can say:

• הוא רוקד מהר
• היא רוקדת מהר

The word מהר stays the same.

That is the normal word order in Hebrew.

Usually, the verb comes first, and then an adverb like מהר follows it:

• רוקד מהר = dances quickly
• מדבר לאט = speaks slowly

So the placement is very natural Hebrew word order.

אבל means but.

It connects two contrasting ideas:

• הוא לא רוקד מהר = he does not dance quickly
• אבל הוא תמיד שמח לרקוד... = but he is always happy to dance...

So it works very much like English but.

In present-tense Hebrew, the verb to be is usually omitted.

So:

• הוא שמח literally looks like he happy
• but it means he is happy

That is completely normal Hebrew.

Compare:

• הוא שמח = he is happy
• הוא היה שמח = he was happy
• הוא יהיה שמח = he will be happy

So only in the present tense is is/am/are usually left out.

שמח means happy or glad, and here it is in the masculine singular form to match הוא.

Compare:

• הוא שמח = he is happy
• היא שמחה = she is happy

In this sentence, שמח לרקוד means something like happy/glad to dance.

לרקוד is the infinitive, meaning to dance.

The prefix ל־ often marks the infinitive in Hebrew, so:

• רוקד = dancing / dances
• לרקוד = to dance

After adjectives like שמח, Hebrew often uses an infinitive to say what someone is happy, glad, ready, or willing to do:

• שמח לעזור = happy to help
• שמח לראות אותך = happy to see you
• שמח לרקוד = happy to dance

תמיד means always.

Here it modifies the whole idea of his being happy to dance:

• הוא תמיד שמח לרקוד = he is always happy to dance

Its position before שמח is very natural. Hebrew often places words like תמיד before the adjective or verb phrase they modify.

Both are possible, and both can mean with his sister.

• עם האחות שלו = with his sister
• עם אחותו = with his sister

The version in your sentence, האחות שלו, is very common in everyday modern Hebrew. It is a more analytic, conversational way to show possession.

The shorter form אחותו is also common, but it can sound a bit more compact, formal, or literary depending on context.

The ה־ is the definite article, meaning the.

So literally:

• האחות שלו = the sister of his

In natural English, that becomes his sister.

The definite article is used because this is a specific, definite person. Compare:

• האחות שלו = his sister / the sister of his
• אחות שלו = a sister of his

So adding ה־ makes it definite.

שלו agrees with the owner, not with the noun being owned.

Here, the owner is he, so you use שלו = his.

Compare:

• האחות שלו = his sister
• האחות שלה = her sister

Even though אחות is a feminine noun, שלו is masculine because the possessor is masculine.

Yes, that is a useful literal breakdown for learning the structure:

• הוא = he
• לא = not
• רוקד = dances / is dancing
• מהר = quickly / fast
• אבל = but
• הוא = he
• תמיד = always
• שמח = happy / glad
• לרקוד = to dance
• עם = with
• האחות שלו = his sister

That literal breakdown helps you see the grammar, even though the natural English translation would sound smoother.