אני רוצה לחזק את המדף לפני שאני שמה עליו את הספרים.

After רוצה (want), Hebrew normally uses the infinitive of the next verb.

So:

• אני רוצה = I want
• לחזק = to strengthen / to reinforce

Together, אני רוצה לחזק means I want to strengthen.

The ל־ at the start of לחזק is the normal marker for the infinitive in Hebrew.

את is a direct object marker. It does not have a separate meaning in English, but it tells you that the next noun is the direct object of the verb.

Hebrew uses את before a definite direct object, such as:

• a noun with ה־ (the)
• a name
• a noun with a possessive ending

So here:

• את המדף = the shelf as a direct object
• את הספרים = the books as a direct object

You would not use את with an indefinite noun:

• אני רוצה לחזק מדף = I want to strengthen a shelf
  (not a specific shelf)

The prefix ה־ is Hebrew for the.

So:

• מדף = a shelf / shelf
• המדף = the shelf
• ספרים = books
• הספרים = the books

In this sentence, the speaker is talking about a specific shelf and specific books, so Hebrew uses the definite form.

Because they are definite direct objects, they also take את:

• את המדף
• את הספרים

We know because of שמה.

Here שמה is the feminine singular present form of לשים (to put).

So:

• אני שם = I put / am putting (male speaker)
• אני שמה = I put / am putting (female speaker)

So this sentence is being said by a female speaker.

A male speaker would say:

אני רוצה לחזק את המדף לפני שאני שם עליו את הספרים.

Yes — the spelling שמה can also mean there in other contexts.

But here it is clearly the verb to put, because it comes after אני and fits the sentence structure:

• אני שמה עליו את הספרים = I put the books on it

So in this sentence, שמה is not the adverb there. It is the feminine verb form putting / put.

This is a very common thing in Hebrew: the same spelling can mean different things, and the context tells you which one it is.

Because לפני ש־ introduces a full clause: before I put...

So Hebrew naturally says:

• לפני שאני שמה עליו את הספרים = before I put the books on it

That clause needs its own subject, so אני appears again.

English does the same thing:

• I want to strengthen the shelf before I put the books on it

You say I twice in English, and Hebrew does too.

This is very common in Hebrew.

In clauses after words like:

• לפני ש־ = before
• אחרי ש־ = after
• כש־ = when

Hebrew often uses the present tense to talk about an action that is still in the future, especially in everyday language.

So:

• לפני שאני שמה עליו את הספרים
  literally looks like before I am putting the books on it
• but naturally means before I put the books on it

This is normal Hebrew usage, not a mistake.

לפני means before.

When Hebrew wants to say before followed by a whole clause, it often uses:

• לפני ש־ = before ...

So:

• לפני שאני שמה עליו את הספרים
  = before I put the books on it

You can think of ש־ here as roughly similar to that in structure, although in natural English we usually just say before I put...

עליו means on it or on him, depending on context.

It is made from:

• על = on
• ־יו = him / it (masculine singular)

So:

• עליו = on him / on it

Here it means on it, referring to המדף (the shelf).

Hebrew often attaches pronouns directly to prepositions:

• עליו = on him / it
• עליה = on her / it
• עליהם = on them (masculine or mixed)
• עליהן = on them (feminine)

Because מדף is a masculine singular noun.

When the pronoun refers back to המדף, Hebrew uses the masculine singular form:

• המדף → עליו = on it

If the noun were feminine, you would use עליה.

For example:

• השולחן is masculine → עליו
• הקופסה is feminine → עליה

So the grammar of עליו agrees with the gender of מדף.

Yes, Hebrew word order is fairly flexible, and both orders can be understood.

This sentence says:

• שמה עליו את הספרים

But Hebrew can also often say:

• שמה את הספרים עליו

Both mean put the books on it.

The version in your sentence is natural and emphasizes the location עליו a bit earlier. Hebrew often moves pieces around more freely than English does, as long as the sentence stays clear.

Yes — but in normal unpointed Hebrew writing, the masculine and feminine singular forms are spelled the same:

• masculine: רוצה
• feminine: רוצה

So by spelling alone, רוצה does not tell you whether the speaker is male or female.

In this sentence, the later verb שמה tells you the speaker is female.

So even though רוצה looks ambiguous in writing, the whole sentence is not ambiguous.

A helpful breakdown is:

• אני רוצה = I want
• לחזק את המדף = to strengthen the shelf
• לפני = before
• שאני שמה עליו את הספרים = I put the books on it

So the pattern is:

subject + want + infinitive + object + before + clause

This is a very common Hebrew sentence pattern, and once you understand the parts, the whole sentence becomes much easier to read.