Tato žárovka je úsporná.

Tato is the feminine singular nominative form of the demonstrative tento, which means this.

Because žárovka is a feminine noun, the demonstrative has to match it:

• tento = masculine
• tato = feminine
• toto = neuter

So:

• tato žárovka = this light bulb

You may also hear more colloquial forms in speech, such as tahle žárovka.
Tenhle would not work here, because that form is masculine.

In Czech, many nouns ending in -a are feminine, and žárovka is one of them.

That matters because other words in the sentence must agree with it:

• tato is feminine
• úsporná is also feminine

So the sentence is a good example of agreement: the demonstrative and adjective both match the noun in gender.

Because adjectives in Czech agree with the noun they describe in gender, number, and case.

Here, žárovka is:

• feminine
• singular
• nominative

So the adjective must also be feminine singular nominative:

• masculine: úsporný
• feminine: úsporná
• neuter: úsporné

For example:

• Ten motor je úsporný.
• Tato žárovka je úsporná.
• To auto je úsporné.

Je is the 3rd person singular present tense of být = to be.

So:

• je = is

In this sentence, it links the subject and the adjective:

• Tato žárovka = subject
• je = is
• úsporná = energy-efficient / economical

Usually, no. In normal Czech sentences, the present tense of být is normally expressed.

So the standard sentence is:

• Tato žárovka je úsporná.

Leaving out je would sound incomplete in ordinary Czech.
You might see omission in very special styles, like headlines or notes, but not in normal learner-style sentences.

It is in the nominative singular, because it is the subject of the sentence.

You can see that both words are nominative:

• tato = feminine singular nominative
• žárovka = feminine singular nominative

If the phrase were an object instead, the forms would change. For example:

• Vidím tuto žárovku. = I see this light bulb.

So:

• nominative: tato žárovka
• accusative: tuto žárovku

Because Czech does not have articles like English.

So Czech does not normally use separate words for:

• a
• an
• the

Whether something is definite or indefinite is usually understood from context, or shown with words like tato if needed.

That means Czech can say simply:

• Žárovka je úsporná.

and context tells you whether it means something like:

• The bulb is energy-efficient
• A bulb is energy-efficient
• This bulb is energy-efficient

A few key points:

• Czech stress is usually on the first syllable of the word.
• Long vowels matter.

Rough pronunciation:

• žárovka ≈ ZHAA-rov-ka
• je ≈ yeh
• úsporná ≈ UU-spor-naa

Useful details:

• ž sounds like the s in measure
• á and ú are long vowels
• j sounds like English y
• Czech r is usually a tapped or rolled r

So the rhythm is roughly:

• ŽÁ-rov-ka je Ú-spor-ná

In standard Czech pronunciation, ú and ů usually represent the same long u sound.

The difference is mostly spelling/history, not meaning here.

A helpful rule:

• ú is used mainly at the beginning of a word or word part
• ů is usually used elsewhere

Since úsporná begins with that sound, it is written with ú.

So in pronunciation, ú and ů are not the important difference; the important thing is that they are both long.

Yes, Czech word order is more flexible than English, but different orders change the emphasis.

The given sentence is natural and neutral:

• Tato žárovka je úsporná.

You could also say:

• Žárovka je úsporná.
  This is also neutral if this is not important.

A more marked order like:

• Úsporná je tato žárovka.

is possible, but it sounds more emphatic or contrastive, like It is this bulb that is energy-efficient.

So for a learner, the original order is a very good default.

Not only. Úsporný / úsporná / úsporné has the broader idea of economical, resource-saving, or efficient in use.

With žárovka, the natural interpretation is energy-efficient or low-energy.
With other nouns, it can refer to saving fuel, money, space, time, and so on.

So the word’s exact nuance depends on the noun it describes.