الشاهد يجلس قرب العروس.

A careful full reading is:

ash-shāhidu yajlisu qurba al-ʿarūsi

In everyday pause pronunciation, learners often hear something closer to:

ash-shāhid yajlis qurb al-ʿarūs

A few notes:

• الشاهد = ash-shāhid
• يجلس = yajlis / yajlisu
• قرب = qurb / qurba
• العروس = al-ʿarūs

The symbol ʿ represents the Arabic letter ع, a throat sound with no exact English equivalent.

Because Arabic has sun letters and moon letters.

• In الشاهد, the letter after ال is ش, which is a sun letter. So the l sound of ال is absorbed, and you pronounce it ash-shāhid, not al-shāhid.
• In العروس, the letter after ال is ع, which is a moon letter. So the l sound stays: al-ʿarūs.

So:

• الشاهد → ash-shāhid
• العروس → al-ʿarūs

الشاهد usually means the witness.

In this sentence, because العروس means the bride, the context may suggest a wedding witness. Depending on context, English might sometimes translate this more naturally as something like the witness or possibly the best man / wedding witness, but the basic literal meaning of شاهد is still witness.

يجلس is the imperfect verb form in Arabic.

In Modern Standard Arabic, the imperfect can express:

• the present: he sits
• an action happening now: he is sitting
• sometimes a habitual action: he sits regularly

So here يجلس could mean:

• sits
• is sitting

The exact choice in English depends on context.

Both are possible in Arabic.

• الشاهد يجلس قرب العروس
• يجلس الشاهد قرب العروس

Both can mean the same thing: The witness sits/is sitting near the bride.

The version starting with الشاهد is often felt as more topic-based: As for the witness, he is sitting near the bride.
The version starting with يجلس is a more straightforward verb-first sentence.

So the sentence you have is completely natural.

Arabic usually does not use a present-tense form of to be the way English does.

But in this sentence, the main point is even simpler: يجلس already means sits / is sitting, so Arabic does not need an extra word for is.

Compare:

• English: The witness is sitting
• Arabic: الشاهد يجلس

No separate present-tense is is needed.

Here قرب means near.

In this structure, قرب العروس literally means something like the vicinity of the bride, but in natural English it simply means near the bride.

So:

• قرب العروس = near the bride

This is a very common Arabic structure.

You may also see:

• بالقرب من العروس = near the bride

Both are correct, but قرب العروس is shorter and more compact.

Because قرب can directly form a construction with the following noun.

So Arabic can say:

• قرب العروس = near the bride

This is normal and idiomatic.

If you use من, you usually get a slightly different expression:

• بالقرب من العروس

So Arabic has more than one way to express near.

In fully vocalized Classical/MSA style, the sentence is:

الشَّاهِدُ يَجْلِسُ قُرْبَ العَرُوسِ

These endings show grammar:

• الشاهدُ: -u because it is the subject/topic
• يجلسُ: -u because it is an indicative imperfect verb
• قربَ: -a because it functions here as an adverbial expression of place
• العروسِ: -i because it is attached to قرب in an iḍāfa-type construction

In normal modern writing, these short vowels are usually not written.

Not all feminine nouns in Arabic end in ة.

عروس means bride, and it is feminine by meaning, even though it does not have ة at the end.

Its masculine counterpart is:

• عريس = groom

So you cannot assume that every feminine noun must end in ة.

Yes.

For example:

• الشاهد يجلس قرب العروس = The witness is sitting near the bride
• الشاهد يجلس بجانب العروس = The witness is sitting beside / next to the bride

The difference is small:

• قرب = near
• بجانب = beside / next to

Both are natural, but بجانب can sound a little more specifically like at the side of.

يجلس comes from the root ج ل س, which is related to sitting.

The basic past-tense verb is:

• جلس = he sat

The imperfect is:

• يجلس = he sits / he is sitting

This root is very common, and you will also see related words built from it.

Not by itself.

يجلس can mean:

• is sitting right now
• sits in a general or habitual sense

Arabic often leaves this to context, while English may force you to choose between sits and is sitting.

So if the meaning has already been given to you as one of those, that is just the translator choosing the most natural English option for the context.