לא משנה כמה החדר מבולגן, אני מסדרת אותו לפני שהאורחים מגיעים.

It is a very common expression meaning no matter how ... or it doesn’t matter how ....

• לא משנה literally means it doesn’t matter
• כמה here adds the idea of how much / how

So לא משנה כמה החדר מבולגן means no matter how messy the room is.

Because in Hebrew, the verb to be is usually not expressed in the present tense.

So:

• החדר מבולגן = the room is messy
• literally: the room messy

This is completely normal Hebrew. In past or future, Hebrew does use forms of to be, but in the present it is usually omitted.

Here כמה means how in the sense of to what degree.

So:

• כמה החדר מבולגן = how messy the room is
• not how many
• not really a literal quantity, but degree

This is why לא משנה כמה works so well as no matter how.

מבולגן is an adjective meaning messy or disorganized, and it has to agree with החדר.

Since:

• חדר is masculine singular
• the adjective must also be masculine singular

So:

• masculine singular: מבולגן
• feminine singular: מבולגנת
• masculine plural: מבולגנים
• feminine plural: מבולגנות

If the noun were החדרָה—which it is not—the form would be different. But with חדר, מבולגן is the correct match.

The prefix ה־ is the Hebrew definite article, meaning the.

So:

• חדר = a room / room
• החדר = the room

and

• אורחים = guests
• האורחים = the guests

In this sentence, the speaker means a specific room and specific guests, so the definite article is used.

מסדרת is the present tense, feminine singular form of the verb לסדר, which means to arrange, organize, tidy up.

So the forms are:

• masculine singular: מסדר
• feminine singular: מסדרת

Because the speaker says אני מסדרת, the sentence suggests that the speaker is female.
If the speaker were male, it would be:

• אני מסדר אותו

It can mean either, depending on context.

Hebrew present tense often covers both:

• I am tidying
• I tidy
• I do tidy

In this sentence, the most natural sense is habitual or regular behavior:

• I tidy it up before the guests arrive

So it is not necessarily describing something happening right this second.

Here אותו means it, referring back to החדר.

So:

• אני מסדרת אותו = I tidy it

Because חדר is a masculine noun, the object pronoun is אותו.

A useful note: אותו can also mean the same when it comes before a noun, as in:

• אותו חדר = the same room

But here, since it stands alone after the verb, it means him/it.

Because אותו already functions as the direct-object form.

With a full definite noun, you would say:

• אני מסדרת את החדר = I tidy the room

But with a pronoun, Hebrew uses forms like:

• אותו = him/it
• אותה = her/it
• אותם / אותן = them

So אני מסדרת אותו is correct, and את אותו would be wrong here.

לפני ש־ means before followed by a clause.

So:

• לפני = before
• לפני ש... = before ... / before that ... happens

In this sentence:

• לפני שהאורחים מגיעים = before the guests arrive

The ש־ connects לפני to the following clause.

Because the conjunction ש־ is usually attached directly to the next word.

So:

• ש + האורחים becomes שהאורחים

This is very normal Hebrew spelling.
It is not a different word; it is just the conjunction ש־ attached to האורחים.

This is a very common Hebrew feature.

מגיעים is literally a present-tense form, but Hebrew often uses the present to talk about:

• scheduled future events
• expected future events
• repeated situations

So לפני שהאורחים מגיעים naturally means before the guests arrive.

In more formal or more explicitly future-oriented Hebrew, you could also hear:

• לפני שהאורחים יגיעו

Both are understandable, but the version with מגיעים sounds very natural in everyday speech, especially in a sentence describing a usual routine.

Because it agrees with האורחים.

• אורח = guest (masculine singular)
• אורחים = guests (masculine plural)

So the verb/adjectival present form must also be masculine plural:

• מגיעים = arrive / are arriving (masculine plural)

If the guests were all female, you would say:

• האורחות מגיעות

Yes. Hebrew allows some flexibility.

The original sentence starts with the no matter how clause for emphasis:

• לא משנה כמה החדר מבולגן, אני מסדרת אותו לפני שהאורחים מגיעים.

You could also say:

• אני מסדרת אותו לפני שהאורחים מגיעים, לא משנה כמה החדר מבולגן.

That still makes sense, but the original order sounds more natural if you want to emphasize however messy the room may be first.