هذه الوحدة جديدة.

• هذه = this for a feminine singular noun
• الوحدة = the unit or the module
• جديدة = new in the feminine singular form

So the structure is literally:

• this
  • the unit
    • new

Natural English: This unit is new.

Because الوحدة is a feminine noun.

In Modern Standard Arabic, this changes depending on gender:

• هذا = this, for masculine singular
• هذه = this, for feminine singular

Since وحدة is feminine, you must say هذه الوحدة.

A big clue is the ending ة, called taa marbuuTa.

Many Arabic nouns ending in ة are feminine, including وحدة. So words that describe it, or point to it, must also be feminine:

• هذه because the noun is feminine
• جديدة because the adjective/predicate must agree with the noun

This is a very common pattern in Arabic.

Arabic adjectives must agree with the noun they describe in gender and usually also in number and definiteness, depending on the structure.

Since الوحدة is:

• singular
• feminine

the word new must also be singular feminine:

• masculine singular: جديد
• feminine singular: جديدة

So:

• الوحدة جديدة = the unit is new
• not الوحدة جديد

In Arabic, the verb to be is usually not stated in the present tense.

So:

• هذه الوحدة جديدة literally looks like this unit new
• but it means This unit is new

This is normal in Arabic nominal sentences.

Compare:

• الوحدة جديدة = The unit is new
• الوحدة كانت جديدة = The unit was new

In the past tense, Arabic does use a verb such as كان.

It is functioning as the predicate of the sentence.

That matters because there is an important difference between:

• هذه الوحدة جديدة = This unit is new
• هذه الوحدة الجديدة = This new unit

In هذه الوحدة جديدة, جديدة is telling you something about الوحدة. It is the predicate of a full sentence.

In هذه الوحدة الجديدة, الجديدة is just modifying الوحدة inside a noun phrase: the new unit.

Because here it is not part of the noun phrase the new unit. Instead, it is the predicate in the sentence The unit is new.

Compare:

• الوحدة جديدة = The unit is new
• الوحدة الجديدة = The new unit

When an adjective directly modifies a definite noun, it usually also becomes definite:

• الوحدة الجديدة = the new unit

But in your sentence, جديدة is not an attributive adjective inside the noun phrase. It is the predicate, so it stays indefinite.

It is a complete sentence in Arabic.

More specifically, it is a nominal sentence, meaning a sentence built without a present-tense verb like is.

The basic structure is:

• هذه الوحدة = the topic / subject part
• جديدة = the comment / predicate part

So yes, this is a full sentence: This unit is new.

A common careful MSA pronunciation is:

• hādhihi al-waḥda jadīda

If full case endings are read aloud very carefully, it can be:

• hādhihi al-waḥdatu jadīdatun

A few pronunciation notes:

• هذه = hādhihi
• ح in وحدة is a deeper h sound than English h
• جديدة = ja-dii-da, with a long ii

In normal reading, case endings are often not pronounced unless the context is very formal.

Because the sentence is talking about a specific unit: this unit.

In Arabic, when you use a demonstrative like هذا or هذه, the noun that follows is commonly definite:

• هذا الكتاب = this book
• هذه الوحدة = this unit

So ال here is expected.

In normal Modern Standard Arabic, the standard form is هذه الوحدة, not هذه وحدة.

After a demonstrative like هذا or هذه, the noun is usually definite:

• هذا البيت = this house
• هذه السيارة = this car
• هذه الوحدة = this unit

So for MSA, هذه الوحدة is the form learners should use.

They look similar, but they mean different things:

• هذه الوحدة جديدة = This unit is new
• الوحدة الجديدة = the new unit

The first is a sentence.
The second is just a noun phrase.

A useful shortcut:

• If the second word is describing the noun inside the same noun phrase, it usually matches in definiteness: الوحدة الجديدة
• If it is the predicate meaning is new, it is usually indefinite: الوحدة جديدة

Yes, in fully vocalized formal Arabic, there would be case endings.

A careful grammatical version would be:

• هذه الوحدةُ جديدةٌ

or more fully in pronunciation:

• hādhihi al-waḥdatu jadīdatun

Here:

• الوحدةُ is nominative
• جديدةٌ is also nominative, because it is the predicate of a nominal sentence

But in everyday printed Arabic, short vowels and case endings are usually omitted, so you normally just see:

• هذه الوحدة جديدة

Yes. Depending on context, وحدة can mean things like:

• unit
• module
• lesson unit
• unity
• oneness

In your sentence, since it is likely from a textbook or course context, الوحدة probably means unit or module.

So هذه الوحدة جديدة would most naturally mean This unit is new.