ينتظر المرشد خلف مدخل المتحف.

In Modern Standard Arabic, it is very common for a sentence to begin with the verb. So ينتظر المرشد is a normal verb–subject order.

This gives a natural, neutral meaning: The guide is waiting.

You could also say:

المرشد ينتظر خلف مدخل المتحف

That is also correct, but it puts a little more focus on the guide as the topic.

ينتظر is in the imperfect form, 3rd person masculine singular.

Depending on context, the Arabic imperfect can mean:

• waits
• is waiting
• sometimes will wait

In this sentence, the most natural reading is is waiting or waits.

Its dictionary form is انتظر = to wait.

Because the subject is المرشد, which is a singular masculine noun meaning the guide.

So:

• ينتظر = he waits / is waiting
• المرشد = the guide

They match in gender and number.

المرشد is the subject of the sentence.

In traditional Arabic grammar, it is the فاعل of ينتظر.

So the basic structure is:

• ينتظر = verb
• المرشد = subject
• خلف مدخل المتحف = phrase telling you where

If the sentence were fully vocalized, this word would normally be:

المُرْشِدُ

with a final -u sound in full formal reading, because it is nominative.

Here خلف means behind.

For a learner, it is fine to think of it as behaving very much like a preposition. In traditional grammar, it is often analyzed as an adverb/noun of place (ظرف مكان), but in practical use it works like this:

خلف + noun
= behind + noun

So:

خلف مدخل المتحف
= behind the entrance of the museum / behind the museum entrance

Because this is an iḍāfa construction, often called the possessive or of-construction.

In Arabic, when two nouns are linked like X of Y, the pattern is:

X + Y

So:

مدخل المتحف
literally = entrance of the museum

A very important rule is that the first noun in an iḍāfa usually does not take ال.

So Arabic says:

• مدخل المتحف = the museum entrance / the entrance of the museum

not:

• المدخل المتحف

Because in an iḍāfa, the definiteness of the whole phrase depends on the second noun.

Here:

• المتحف = the museum (definite)

That makes the whole phrase مدخل المتحف definite as well:

• مدخل المتحف = the entrance of the museum / the museum entrance

So even without ال on مدخل, the whole expression is still definite.

This sentence contains a nested structure.

A full grammatical breakdown is:

• ينتظر = verb
• المرشد = subject
• خلف = adverb/preposition-like word meaning behind
• مدخل = noun following خلف
• المتحف = second noun in the iḍāfa

In full formal grammar:

• خلفَ is usually treated as a ظرف and is in the accusative
• مدخلِ is genitive because it is attached to خلف
• المتحفِ is genitive because it is the second term of the iḍāfa with مدخل

So the chain is:

خلفَ مدخلِ المتحفِ

You do not usually see these case vowels in normal writing, but they are there grammatically.

A fully vocalized version is:

يَنْتَظِرُ الْمُرْشِدُ خَلْفَ مَدْخَلِ الْمَتْحَفِ

A rough pronunciation guide is:

yantaẓiru al-murshidu khalf(a) madkhali al-matḥafi

In normal pausal reading, speakers often drop the final case vowels, so it may sound more like:

yantaẓir al-murshid khalf madkhal al-matḥaf

Good question. In Arabic, انتظر can take a direct object:

• أنتظر الحافلة = I am waiting for the bus

But it can also be used without stating the thing or person being waited for, if that is not important.

So here:

ينتظر المرشد خلف مدخل المتحف

simply means that the guide is waiting and tells you where he is waiting. The sentence does not say what or whom he is waiting for, and that is perfectly normal.