אני רוצה לשים את הספר על המדף.

The sentence follows a very natural Hebrew pattern:

אני + רוצה + לשים + את הספר + על המדף

That is:

• אני = I
• רוצה = want
• לשים = to put
• את הספר = the book
• על המדף = on the shelf

So the structure is basically:

subject + want + infinitive + object + location

This is very close to the English structure I want to put the book on the shelf.

Yes. In unpointed Hebrew, רוצה can represent two different spoken forms:

• רוֹצֶה (rotze) = said by a male
• רוֹצָה (rotsa) = said by a female

So:

• A male speaker says: אני רוצה לשים את הספר על המדף
• A female speaker also writes: אני רוצה לשים את הספר על המדף

The spelling stays the same, but the pronunciation changes.

Because after רוצה (want), Hebrew usually uses an infinitive, just like English uses to + verb:

• I want to put
• אני רוצה לשים

The word לשים means to put.

So רוצה לשים is literally want to put.

In this case, the ל־ is part of the infinitive form.

A very common way to think about it is:

• לשים = to put
• לכתוב = to write
• ללכת = to go

So the ל־ often corresponds to English to when introducing a verb in the infinitive.

That does not mean every ל־ always means to in exactly the same way, but here that is the right idea.

את is the definite direct object marker.

Hebrew uses את before a direct object when that object is definite, meaning things like:

• the book
• this book
• my book
• a proper name, like David

Here, הספר means the book, which is definite, so Hebrew adds את:

• את הספר = the book as a direct object

Important: את usually is not translated into English. It is a grammatical marker.

The prefix ה־ is the Hebrew word for the.

So:

• ספר = book
• הספר = the book

Likewise:

• מדף = shelf
• המדף = the shelf

So both nouns in the sentence are definite:

• הספר = the book
• המדף = the shelf

Because הספר is the direct object of the verb לשים (to put), but המדף is not.

In this sentence:

• את הספר = the thing being put
• על המדף = the place where it is being put

Since המדף comes after the preposition על (on), it is part of a prepositional phrase, not a direct object. Hebrew does not use את there.

So:

• לשים את הספר = to put the book
• על המדף = on the shelf

A common pronunciation is:

• ani rotze lasim et ha-sefer al ha-madaf
  if a male is speaking

• ani rotsa lasim et ha-sefer al ha-madaf
  if a female is speaking

A few stress notes:

• a-NI
• rot-ZE / rot-SA
• la-SIM
• SE-fer
• ma-DAF

So the sentence rhythm is roughly:

a-NI rot-ZE la-SIM et ha-SE-fer al ha-ma-DAF

Sometimes, yes, especially in conversation if the subject is already obvious from context.

But with רוצה, Hebrew often keeps the subject pronoun because the form by itself does not clearly show person the way some past or future forms do.

So:

• אני רוצה לשים את הספר על המדף = clear and standard
• רוצה לשים את הספר על המדף = possible in context, more conversational

For learners, it is safest to include אני.

Because על means on, which matches the English idea of putting something on the shelf.

• על המדף = on the shelf
• במדף = in the shelf / inside the shelf

Usually, if you mean placing a book on a shelf, על המדף is the natural choice.

If you said במדף, it would sound like you mean inside some shelf space or compartment, which is a different image.

It is a very common verb, but learners often notice that its forms do not feel perfectly regular at first.

Some useful forms are:

• לשים = to put
• שם = puts / is putting (masculine singular)
• שמה = puts / is putting (feminine singular)
• שמים = put / are putting (masculine plural or mixed)
• שמות = put / are putting (feminine plural)

So if you later see forms like אני שם את הספר על המדף, that means I am putting / I put the book on the shelf (said by a male).

In your sentence, though, you only need לשים because it comes after רוצה.

Yes, Hebrew word order is somewhat flexible, but the version you have is the most neutral and natural:

אני רוצה לשים את הספר על המדף.

You may hear other orders for emphasis, for example:

• את הספר אני רוצה לשים על המדף.

That gives extra emphasis to the book.

But for a learner, the original order is the best default choice.