هذه حملة تنظيف.

A simple breakdown is:

• هذه = this (used with a feminine singular noun)
• حملة = campaign, drive
• تنظيف = cleaning, clean-up

So the sentence is literally something like:

• This [is a] cleaning campaign

In natural English, that becomes This is a cleaning campaign.

Because حملة is a feminine singular noun in Arabic.

A very common sign of feminine nouns is the ending ة (called tāʾ marbūṭa), and حملة has that ending. Since the demonstrative has to agree with the noun, Arabic uses:

• هذا for masculine singular
• هذه for feminine singular

So:

• هذه حملة = This is a campaign
• not هذا حملة

In Arabic, the present tense to be is usually not expressed in sentences like this.

So Arabic often says:

• هذه حملة تنظيف

where English says:

• This is a cleaning campaign

This is called a nominal sentence. Arabic simply places the parts next to each other, and the meaning is is understood.

If you wanted a past tense, then Arabic would use a verb, for example:

• كانت هذه حملة تنظيف = This was a cleaning campaign

Yes. حملة تنظيف is an iḍāfa structure, often translated as a cleaning campaign or literally a campaign of cleaning.

In an iḍāfa:

• the first noun is the thing being described: حملة
• the second noun specifies what kind: تنظيف

So:

• حملة تنظيف = cleaning campaign
• literally: campaign of cleaning

Arabic uses iḍāfa very often where English uses noun + noun combinations, like:

• book cover
• school bus
• city center

Because in an iḍāfa, the first noun does not take tanwīn.

So although the phrase is indefinite in meaning here, you do not write:

• حملةٌ تنظيفٍ

Instead, the correct fully vocalized form is:

• حملةُ تنظيفٍ

That is normal for iḍāfa:

• first noun: no ال
• first noun: no tanwīn
• second noun: usually shows the definiteness/indefiniteness of the whole phrase

So:

• حملةُ تنظيفٍ = a cleaning campaign
• حملةُ التنظيفِ = the cleaning campaign

تنظيف is a verbal noun (also called a maṣdar). It comes from the verb:

• نظّف = to clean

So تنظيف means:

• cleaning
• clean-up
• the act/process of cleaning

Arabic often uses verbal nouns in places where English might use:

• a gerund: cleaning
• a noun modifier: cleaning campaign
• or a phrase like campaign for cleaning up

That is why تنظيف works very naturally here.

A fully vocalized version would be:

• هٰذِهِ حَمْلَةُ تَنْظِيفٍ

Here is what is happening grammatically:

• هٰذِهِ = demonstrative, feminine singular
• حَمْلَةُ = nominative, because it is the predicate of the sentence
• تَنْظِيفٍ = genitive, because it is the second term of the iḍāfa

So if you are studying case endings, this sentence is a good example of:

• a nominal sentence
• with a predicate that is an iḍāfa phrase

This is because ة is tāʾ marbūṭa.

When a word ends there, it is often pronounced as -a in pause:

• حملة = ḥamla

But when the word is connected grammatically to something after it, especially in iḍāfa or with case endings, the t sound appears:

• حملةُ تنظيفٍ = ḥamlatu tanẓīfin
• or in a pause-style reading, often something like ḥamlat tanẓīf

So learners are often surprised that ة is not always just -a. In connected MSA reading, it can surface as t.

A careful MSA pronunciation with case endings is approximately:

• hādhihi ḥamlatu tanẓīfin

If you pause at the end and do not strongly pronounce final case endings, you may hear something closer to:

• hādhihi ḥamlat tanẓīf

A few sound notes:

• ح in حملة is a deep breathy sound, not the ordinary English h
• ظ in تنظيف is an emphatic consonant, deeper than ordinary z
• هذه is pronounced hādhihi, not just hādhā

Yes. Arabic has several natural ways to express a similar idea, depending on style and nuance.

For example:

• هذه حملة تنظيف = This is a cleaning campaign
• هذه حملةٌ للتنظيف = This is a campaign for cleaning
• هذه حملةُ تنظيفِ الشاطئِ = This is a beach-cleaning campaign

The version you have, هذه حملة تنظيف, is very normal and compact, especially in formal written Arabic such as signs, campaigns, announcements, or educational materials.