عقد الإيجار ينتهي غدا.

A helpful pronunciation is:

ʿaqd al-ʾījār yantahī ghadan

A few notes:

• ع in عقد is the letter ʿayn, a sound English does not have.
• خ/غ? Here you have غ in غدا, pronounced like a deep, voiced French-style r for many learners.
• ينتهي is pronounced yan-ta-hī.

If you include full case endings in careful MSA, it would be closer to:

ʿaqdu l-ʾījāri yantahī ghadan

Literally:

• عقد = contract
• الإيجار = the renting / the lease

So عقد الإيجار literally means the contract of the lease/rental, which in natural English is the lease contract, the rental contract, or the lease agreement.

Because عقد الإيجار is an iḍāfa construction, often called a construct phrase.

In an iḍāfa:

• the first noun does not take الـ
• the second noun can make the whole phrase definite

So:

• عقد = contract
• الإيجار = the lease/rental

Together, عقد الإيجار means the lease contract, even though only the second word has الـ.

This is very common in Arabic:

• كتاب الطالب = the student’s book
• باب البيت = the door of the house

ينتهي means ends, comes to an end, or expires, depending on context.

In this sentence, the most natural English meaning is:

• ends tomorrow
• or expires tomorrow

This verb is especially common for things like:

• contracts
• deadlines
• meetings
• terms or periods of time

So عقد الإيجار ينتهي غدا can mean that the lease contract reaches its end tomorrow.

ينتهي is the imperfect tense form of انتهى.

So:

• انتهى = it ended / it came to an end
• ينتهي = it ends / it is ending

It is a 3rd person masculine singular form, matching عقد, which is a masculine singular noun.

You may also notice the related noun:

• نهاية = end

So these words belong to the same general family of meaning.

Because in Arabic, the imperfect tense often covers:

• present time
• near future
• scheduled future

So ينتهي غدا naturally means ends tomorrow.

Arabic does not always need a separate future marker when the time word already makes the future clear. Since غدا means tomorrow, the future meaning is obvious.

If you want to make the future even more explicit, you could say:

• سينتهي عقد الإيجار غدًا
• سوف ينتهي عقد الإيجار غدًا

Both mean the lease contract will end tomorrow.

This is a very useful distinction.

• ينتهي = it ends / it comes to an end
• يُنهي = he/it ends something / terminates something

So:

• عقد الإيجار ينتهي غدًا = The lease contract ends tomorrow
• الشركة تُنهي عقد الإيجار غدًا = The company terminates the lease contract tomorrow

In other words:

• ينتهي is usually intransitive
• يُنهي is transitive

The sentence uses ينتهي because the contract itself is the thing coming to an end.

Arabic often does not use a present-tense verb meaning is/are the way English does.

But in this particular sentence, the main predicate is already a verb:

• ينتهي = ends

So Arabic does not need anything like is here.

The structure is basically:

• عقد الإيجار = the lease contract
• ينتهي غدا = ends tomorrow

Arabic is simply saying:

• The lease contract ends tomorrow

not

• The lease contract is ending tomorrow

though that can be an English translation too, depending on context.

It is commonly analyzed as a nominal sentence because it begins with a noun phrase:

• عقد الإيجار = the subject/topic

Then the predicate is a verbal clause:

• ينتهي غدا = ends tomorrow

So a simple way to understand it is:

• topic: the lease contract
• comment about it: ends tomorrow

Arabic often allows this kind of structure very naturally.

غدا / غدًا means tomorrow, and here it functions as an adverb of time.

In fully vocalized MSA, it is written:

• غدًا

The final tanwīn fatḥ shows the adverbial accusative form.

In ordinary unvocalized writing, short vowels are usually omitted, so you often see:

• غدا

That is normal.

So:

• غدا = normal unvocalized spelling
• غدًا = fully vocalized spelling

The fully vowelled form is:

عقدُ الإيجارِ ينتهي غدًا

Those endings show the grammar:

• عقدُ = nominative, because it is the main subject/topic
• الإيجارِ = genitive, because it is the second noun in the iḍāfa
• غدًا = accusative adverb of time

In most everyday writing, these short vowels are simply not written.

Yes. Arabic word order is flexible.

This sentence can also appear as:

• ينتهي عقد الإيجار غدًا
• غدًا ينتهي عقد الإيجار

The basic meaning stays the same, but the emphasis changes a little:

• عقد الإيجار ينتهي غدًا
  Focuses first on the lease contract

• ينتهي عقد الإيجار غدًا
  Feels more directly verbal: The lease contract ends tomorrow

• غدًا ينتهي عقد الإيجار
  Gives extra emphasis to tomorrow

All are natural in the right context.