סבתא כתבה לי ברכה חמה, ואני רוצה לשמור אותה בתוך הספר.

Because the subject סבתא is grammatically feminine singular, and in the past tense Hebrew verbs agree with the subject in gender and number.

• כתב = he wrote
• כתבה = she wrote

So סבתא כתבה means Grandma wrote.

לי means to me or for me.

It is made from:

• ל־ = to / for
• י = me

So כתבה לי is literally wrote to me / wrote for me. In natural English, this often becomes wrote me or wrote to me, depending on context.

ברכה literally means blessing, but in everyday Hebrew it can also mean a greeting, greeting message, or a warm written note.

In this sentence, it most likely means a kind, heartfelt written message, not necessarily a religious blessing.

Because adjectives in Hebrew usually agree with the noun they describe in gender and number.

• ברכה is feminine singular
• so the adjective must also be feminine singular: חמה

Compare:

• חם = masculine singular
• חמה = feminine singular

So ברכה חמה means a warm blessing/message.

Because the conjunction ו־ meaning and is usually attached directly to the following word.

So:

• ו = and
• אני = I
• ואני = and I

This is completely normal in Hebrew spelling.

Not in unpointed Hebrew spelling. רוצה can represent both:

• masculine singular: rotze
• feminine singular: rotsa

So from the spelling alone, you cannot tell whether the speaker is male or female. You would know only from context or from vowel marking.

Because after רוצה = want, Hebrew normally uses the infinitive, just like English uses to + verb.

• רוצה לשמור = want to keep
• לשמור = to keep / to save / to preserve

This is a very common pattern:

• אני רוצה לאכול = I want to eat
• אני רוצה ללכת = I want to go

Because אותה refers back to ברכה, and ברכה is feminine.

Hebrew object pronouns agree with the noun they replace:

• אותו = him / it for masculine nouns
• אותה = her / it for feminine nouns

So here אותה means it, referring to the feminine noun ברכה.

Because אותה already functions as a direct object pronoun by itself.

Compare:

• אני שומר את הספר = I keep the book
• אני שומר אותו = I keep it

When Hebrew uses a full definite noun as a direct object, it often needs את. But with object pronouns like אותו / אותה / אותם / אותן, you do not add a separate את before them.

בתוך הספר is more specific and means inside the book or within the book.

• בספר can mean in the book, but that might sometimes sound less physically specific
• בתוך הספר clearly emphasizes being placed inside it

Here it sounds like the speaker wants to keep the note physically tucked into the book.

הספר means the book, so it takes the definite article ה־.

But סבתא here is being used like Grandma, almost like a name or family title, so it does not need ה־.

Compare the idea in English:

• Grandma wrote me a note
  not
• The grandma wrote me a note

So סבתא here is definite by context, without the article.

Yes, it is very natural.

The order is:

• subject: סבתא
• verb: כתבה
• indirect object: לי
• direct object: ברכה חמה

Hebrew word order is somewhat flexible, but this sentence sounds completely normal and natural. The second clause is also straightforward:

• ואני רוצה לשמור אותה בתוך הספר
• and I want to keep it inside the book

Yes. לשמור is a broad verb that can mean:

• to keep
• to save
• to preserve
• to guard
• to watch over

In this sentence, the most natural meaning is to keep or to preserve, because the speaker wants to hold on to the written message.