Tato činnost je důležitá.

Tato means this.

It is the feminine singular nominative form of the Czech demonstrative ten / ta / to.

In this sentence, činnost is a feminine singular noun, so the demonstrative must match it:

• masculine: ten
• feminine: ta / tato
• neuter: to

So:

• tato činnost = this activity

The longer form tato is a more explicit form of ta. In many contexts, ta can mean that or simply the one, while tato clearly means this.

Činnost is a noun meaning activity, operation, or functioning, depending on context.

In this sentence, it most naturally means activity.

It is a feminine noun. That matters because other words in the sentence must agree with it, especially:

• tato → feminine singular
• důležitá → feminine singular

Because it has to agree with činnost.

Důležitý means important, but Czech adjectives change their endings to match the noun in gender, number, and case.

Here, činnost is:

• feminine
• singular
• nominative

So the adjective must also be feminine singular nominative:

• masculine: důležitý
• feminine: důležitá
• neuter: důležité

So:

• důležitá činnost = an important activity
• činnost je důležitá = the activity is important

Je means is. It is the 3rd person singular present form of být (to be).

So:

• Tato činnost je důležitá. = This activity is important.

In normal standard Czech, you usually do not omit je in this kind of sentence. English and Czech are similar here: you need the verb to be.

It is in the nominative case.

That is because činnost is the subject of the sentence:

• Tato činnost = the thing being talked about
• je důležitá = is important

The predicate adjective důležitá also appears in nominative form because it describes the subject after je.

Yes, Czech word order is more flexible than English.

The neutral, most straightforward order is:

• Tato činnost je důležitá.

But other orders are possible, especially for emphasis:

• Důležitá je tato činnost. = It is this activity that is important.
• Je důležitá tato činnost? = Is this activity important? or a marked statement, depending on intonation

Even though Czech allows flexibility, the original order is the most natural basic statement for learners.

Because Czech does not have articles like English the and a/an.

Whether something is definite or indefinite is usually understood from:

• context
• word order
• demonstratives like tato (this)

So Czech can say simply:

• činnost je důležitá = the activity is important / an activity is important, depending on context

When you add tato, it becomes specifically:

• tato činnost = this activity

A rough pronunciation guide:

• č sounds like ch in church
• ž sounds like the s in measure
• ů is a long oo sound
• í and á are long vowels

Approximate pronunciations:

• činnost ≈ CHIN-nost
• důležitá ≈ doo-LEH-zhi-taa

A few important notes:

• Czech stress is usually on the first syllable of the word.
• Vowel length matters, so á, í, ů are pronounced longer than a, i, u.

Both can refer to this activity, but tato is more clearly and explicitly demonstrative.

Very roughly:

• ta činnost = that activity or sometimes the activity / this activity, depending on context
• tato činnost = this activity

For learners, a helpful rule is:

• use tato when you want a clear this
• use ta with care, because it can be less precise and more context-dependent

Because Czech uses agreement much more than English.

The noun činnost is feminine singular nominative, so words connected to it must often match that form:

• demonstrative: tato
• adjective/predicate adjective: důležitá

This is a core feature of Czech grammar. English does not do much of this, but Czech does it constantly.

Yes. The pattern is:

• This + noun + is + adjective
• in Czech: [demonstrative] + [noun] + je + [adjective agreeing with the noun]

Examples:

• Tato kniha je zajímavá. = This book is interesting.
• Tato práce je těžká. = This work/job is difficult.

Because kniha, práce, and činnost are feminine singular, the forms stay feminine:

• tato
• zajímavá / těžká / důležitá

If the noun changes gender, the other words change too:

• Ten problém je důležitý. = This problem is important.
• To rozhodnutí je důležité. = This decision is important.