Моя любимая блузка мнётся меньше, чем новая рубашка.

Because they are all feminine singular nominative forms.

The nouns блузка and рубашка are both feminine singular nouns, so the words describing them have to agree with them:

• моя любимая блузка
• новая рубашка

In Russian, adjectives and possessive words usually agree with the noun in gender, number, and case.

They are in the nominative case.

• блузка is the subject of the sentence.
• рубашка is also nominative because the comparison is really short for:

Моя любимая блузка мнётся меньше, чем новая рубашка мнётся.

The second мнётся is omitted because it is understood.

Мнётся is the 3rd person singular present tense form of мяться.

So:

• мяться = to get creased, to wrinkle easily, to crumple
• мнётся = wrinkles / gets creased

It is used especially for fabrics, clothes, paper, and similar things.

So блузка мнётся means the blouse wrinkles / gets wrinkled.

The -ся makes the verb reflexive.

With clothing and fabric, Russian often uses a reflexive verb where English uses an ordinary intransitive verb:

• рубашка мнётся = the shirt wrinkles
• literally, it is something like the shirt creases itself / gets creased

You do not need a direct object here. The item itself is what gets wrinkled.

Because меньше here is an adverbial comparative: it tells you to a lesser degree the blouse wrinkles.

It modifies the verb:

• мнётся меньше = wrinkles less

Compare the English pattern:

• The blouse wrinkles less
• not The blouse is less wrinkly in this sentence

So меньше is the natural word here.

Чем means than in comparisons.

So:

• меньше, чем новая рубашка = less than a new shirt

A fuller version would be:

• Моя любимая блузка мнётся меньше, чем новая рубашка мнётся.

Russian often leaves out repeated words when they are obvious.

Because чем introduces the comparison part, and in Russian this is normally separated by a comma.

So:

• мнётся меньше, чем новая рубашка

This is standard punctuation in Russian comparisons of this type.

Меньше is the normal, everyday word here.

• меньше = less
• менее = less / less so, but usually more formal or bookish

In a simple sentence about clothes, мнётся меньше sounds natural.
Менее would sound more formal and would usually appear in slightly different structures.

Because it expresses a general property of the blouse, not something happening only right now.

Russian often uses the present tense for general truths or typical behavior:

• Эта ткань быстро сохнет. = This fabric dries quickly.
• Рубашка мнётся. = The shirt wrinkles easily.

So here the meaning is something like:

My favorite blouse tends to wrinkle less than a new shirt.

Yes. With things, любимый / любимая / любимое often means favorite.

So:

• любимая блузка = favorite blouse

With people, it can mean beloved or dear, depending on context.
But for clothing, favorite is the natural interpretation.

Usually:

• блузка = blouse
• рубашка = shirt

Both are items of clothing, but блузка is typically a blouse-style top, while рубашка is a shirt.

A learner may also notice that both are feminine nouns, even though the English words do not have grammatical gender.

A rough learner-friendly pronunciation is:

mnyó-tsya

A few useful points:

• ё is always stressed
• тс sounds like ts
• -ся at the end is pronounced roughly -sya here

Also, many Russian texts write е instead of ё, so you may see мнется, but it is still pronounced мнётся.

No, Russian word order is fairly flexible, but this sentence has a neutral, natural order:

• Моя любимая блузка мнётся меньше, чем новая рубашка.

This starts with the thing being discussed, then the verb, then the comparison.

You can change word order for emphasis, but the given version is the most straightforward.

Because Russian does not have articles.

So новая рубашка can mean:

• a new shirt
• the new shirt

The exact meaning depends on context. English has to choose; Russian usually does not.

Not in this sentence.

Мнётся here means wrinkles / gets wrinkled / creases easily, not is already wrinkled.

So the sentence is about how easily the clothes wrinkle, not about their current condition.

If you wanted to say is wrinkled, you would use a different structure.