Čistota je důležitá.

Because čistota is a feminine singular noun, and Czech adjectives must agree with the noun they describe.

• čistota = feminine singular
• so the adjective must also be feminine singular
• that gives důležitá

Compare:

• čistota je důležitá = cleanliness is important
• pořádek je důležitý = order is important (pořádek is masculine)
• jídlo je důležité = food is important (jídlo is neuter)

Je is the 3rd person singular form of the verb být (to be).

So:

• já jsem = I am
• ty jsi = you are
• on / ona / ono je = he / she / it is

In Čistota je důležitá, je simply means is.

Czech has no articles.

So Czech does not normally use words equivalent to English a, an, or the.

That means:

• čistota can mean cleanliness
• depending on context, Czech often leaves definiteness unstated

This is completely normal. Czech speakers understand the meaning from context, not from articles.

It is a noun.

• čistý / čistá / čisté = clean (adjective)
• čistota = cleanliness (noun)

So the sentence is structured like:

• Čistota = cleanliness
• je = is
• důležitá = important

A useful pattern is:

• adjective: čistý = clean
• abstract noun: čistota = cleanliness

Because after být (to be), Czech often uses the nominative for predicate adjectives.

In this sentence:

• čistota is nominative
• důležitá is also nominative

So Čistota je důležitá literally works like Cleanliness is important, where both parts are in the basic form.

This is one of the most common sentence patterns in Czech.

A rough pronunciation guide:

• Č = like ch in check
• čistota ≈ CHIS-to-ta
• je ≈ ye
• důležitá ≈ DOO-le-zhi-taa

A few details:

• ž sounds like the s in measure
• ů is pronounced like a long oo
• Czech stress usually falls on the first syllable:
  • ČIStota
  • DŮležitá

So the rhythm is roughly: CHIS-to-ta ye DOO-le-zhi-taa

In modern Czech, ů and ú are pronounced the same: both are a long ú sound.

The difference is mainly historical and spelling-based:

• ú usually appears at the beginning of a word or part of a word
• ů usually appears elsewhere

So in důležitá, the ů is just the normal spelling for that word. You do not pronounce it differently from ú.

Yes, Czech word order is more flexible than English, but the basic order here is the most neutral:

• Čistota je důležitá.

You may also hear:

• Důležitá je čistota.

That version puts more emphasis on important or on cleanliness as the key point.

So:

• Čistota je důležitá. = neutral statement
• Důležitá je čistota. = more emphasis, a bit like What is important is cleanliness

Normally, in standard Czech, no.

In the present tense, Czech usually keeps the verb je in sentences like this:

• Čistota je důležitá.

In some informal styles, headlines, or very compressed expressions, Czech may omit forms of to be, but for normal learner Czech you should keep je here.

So the correct full sentence is:

• Čistota je důležitá.

You negate je by changing it to není:

• Čistota není důležitá. = Cleanliness is not important.

So:

• je = is
• není = is not

This is the standard way to negate sentences with být in the present tense.

You can add velmi (very):

• Čistota je velmi důležitá.

You could also use:

• Čistota je hodně důležitá. = Cleanliness is very/really important.
• Čistota je opravdu důležitá. = Cleanliness is really important.

The most neutral textbook version is:

• Čistota je velmi důležitá.

It mainly means cleanliness, that is, the state or quality of being clean.

If you want to say cleaning as an action, Czech usually uses a different word, such as:

• čištění = cleaning, cleansing
• sometimes úklid = tidying, cleaning up

So:

• čistota je důležitá = cleanliness is important
• this does not mean cleaning is important in the action sense as directly

Yes, it is very helpful to memorize Czech nouns together with their gender.

Čistota is feminine, and that affects:

• adjective endings
• pronouns
• sometimes past tense forms and other agreement patterns

A useful habit is to learn vocabulary like this:

• ta čistota = the cleanliness

That ta reminds you it is feminine.

It is in the nominative singular.

This is the dictionary form of the noun, and it is used because čistota is the subject of the sentence:

• Čistota = the subject
• je = the verb
• důležitá = predicate adjective agreeing with the subject

So if you look the word up, you will find it as čistota.