יש לי חצאית ורודה עם כיס קטן, אבל אני לא מוצאת את החגורה שלה.

Hebrew usually expresses possession with יש ל־... literally there is to....

So:

• יש לי = literally there is to me
• natural meaning: I have

In this sentence:

• יש לי חצאית ורודה = I have a pink skirt

This is the normal everyday way to say I have in Hebrew.

Because חצאית is a feminine noun, and adjectives must agree with the noun in gender and number.

• ורוד = masculine singular
• ורודה = feminine singular

So:

• חצאית ורודה = a pink skirt

If the noun were masculine, you would use ורוד instead.

Because כיס is a masculine noun.

So the adjective must also be masculine:

• כיס קטן = a small pocket

Even though חצאית is feminine, the adjective קטן describes כיס, not חצאית.
That is why the gender changes.

In Hebrew, adjectives usually come after the noun they describe.

So Hebrew says:

• חצאית ורודה = literally skirt pink
• כיס קטן = literally pocket small

This is the normal adjective position in Hebrew.

מוצאת is the feminine singular present-tense form of the verb למצוא = to find.

So:

• אני מוצאת = I find / I am finding said by a female speaker
• אני לא מוצאת = I do not find / I can’t find said by a female speaker

Hebrew present tense agrees with the gender of the speaker in first person too.

If a male speaker said the same sentence, it would be:

• אני לא מוצא

Literally, it is I am not finding.
But in natural English, the best translation is often I can’t find.

So in context:

• אבל אני לא מוצאת את החגורה שלה
  naturally = but I can’t find its belt

Hebrew often uses simple present tense where English prefers can’t.

את is the marker of a definite direct object.

It appears before a direct object that is definite, for example:

• with ה־: את החגורה
• with a name: את דנה
• with a possessive/clearly specific object in many cases

Here, החגורה means the belt, so it is definite.
That is why Hebrew uses את:

• אני לא מוצאת את החגורה = I can’t find the belt

Important: את is usually not translated into English.

Because the sentence is talking about a specific belt: the belt that belongs to the skirt.

So:

• חגורה = a belt
• החגורה שלה = its belt / her belt, meaning a particular one

That makes it definite, so ה־ is used.

שלה usually means hers, her, or its, depending on context.

In this sentence, it refers to the skirt:

• החגורה שלה = its belt / literally her belt

Hebrew uses these possessive forms even for inanimate things, so שלה can refer to an object like a skirt.

You could think of it as:

• the skirt’s belt
• its belt

Because it refers back to חצאית, and חצאית is feminine.

Hebrew possessive forms agree with the possessor:

• שלו = his / its for a masculine noun
• שלה = her / its for a feminine noun

Since the skirt is feminine:

• החגורה שלה = its belt

Yes. Both are possible.

• החגורה שלה = its belt
• החגורה של החצאית = the belt of the skirt / the skirt’s belt

The version with שלה is shorter and very natural when the reference is clear.

Because those nouns are indefinite here.

• חצאית ורודה = a pink skirt
• כיס קטן = a small pocket

If they were definite, you would expect ה־:

• החצאית הוורודה = the pink skirt
• הכיס הקטן = the small pocket

So the sentence contrasts:

• a pink skirt
• a small pocket
• but the belt

Because once the skirt has been introduced, Hebrew can refer back to it with שלה = its/her.

So the sentence flows naturally:

• I have a pink skirt with a small pocket, but I can’t find its belt.

This avoids unnecessary repetition of חצאית.

Only the first-person present-tense verb form would change.

Female speaker:

• אני לא מוצאת

Male speaker:

• אני לא מוצא

The rest of the sentence can stay the same, because:

• חצאית is still feminine
• ורודה still agrees with חצאית
• כיס קטן still agrees with כיס
• שלה still refers to חצאית

So a male speaker would say:

• יש לי חצאית ורודה עם כיס קטן, אבל אני לא מוצא את החגורה שלה.

Yes. עם כיס קטן describes the skirt:

• חצאית ורודה עם כיס קטן = a pink skirt with a small pocket

The preposition עם means with, and it adds more description to the noun phrase.
So the whole first part means:

• I have a pink skirt that has a small pocket

This is a very common Hebrew structure.