Gledatelj čita najavu u gledalištu.

Because najavu is the direct object of čita.

The verb čitati takes an object in the accusative case, so the noun najava changes:

• nominative: najava
• accusative: najavu

This is a regular pattern for many feminine nouns ending in -a:

• knjiga → knjigu
• poruka → poruku
• najava → najavu

So čita najavu means reads an/the announcement.

Because u here means in, describing a location, and that requires the locative case.

So:

• dictionary form: gledalište
• locative singular: gledalištu

This is the pattern in the sentence:

• u gledalištu = in the auditorium / in the seating area

A very useful rule is:

• u + locative = location, being somewhere
• u + accusative = movement into somewhere

Compare:

• On je u gledalištu. = He is in the auditorium.
• On ulazi u gledalište. = He is going into the auditorium.

Gledatelj is in the nominative singular because it is the subject of the sentence — the person doing the action.

Here is the structure:

• Gledatelj = subject
• čita = verb
• najavu = object
• u gledalištu = location

So gledatelj stays in its basic dictionary form here.

Čita is:

• present tense
• 3rd person singular
• from the infinitive čitati = to read

So it corresponds to:

• he reads
• she reads
• it reads

Since Croatian usually does not need subject pronouns, the verb form itself already tells you it is 3rd person singular. In this sentence, gledatelj tells you who that person is.

Yes. Very often, the Croatian present tense can cover both ideas, and context tells you which one is meant.

So čita can mean:

• reads
• is reading

For example:

• Gledatelj čita najavu. could mean
  
  • The spectator reads the announcement
    or
  • The spectator is reading the announcement

If you need to make the ongoing action especially clear, Croatian usually relies on context or extra words rather than a separate tense like English does.

Because Croatian does not have articles.

English uses:

• a spectator
• the spectator

Croatian usually just says:

• gledatelj

The same is true for the object:

• najavu can mean an announcement or the announcement, depending on context.

If you want to make the meaning more specific, Croatian uses other tools, such as:

• word order
• context
• demonstratives like taj = that
• jedan sometimes for a certain / one

Examples:

• Taj gledatelj čita najavu. = That spectator is reading the announcement.
• Jedan gledatelj čita najavu. = A spectator / one spectator is reading the announcement.

Croatian word order is fairly flexible. The sentence as given is a neutral, straightforward order:

• Gledatelj čita najavu u gledalištu.

But other orders are possible, with changes in emphasis:

• U gledalištu gledatelj čita najavu.
  Emphasizes the location.

• Najavu gledatelj čita u gledalištu.
  Emphasizes najavu.

• Gledatelj u gledalištu čita najavu.
  Slightly highlights gledatelj in the auditorium.

So the meaning stays broadly similar, but the focus shifts.

They are related words built from the same root, connected with gledati = to watch / look.

• gledatelj = viewer, spectator
  a person who watches

• gledalište = auditorium, seating area, place where people watch
  the place from which people watch

So they are related in meaning, but they are different kinds of words:

• -telj often makes a noun for a person
• -ište often makes a noun for a place

That is why they look similar.

Not usually. Gledalište most often means the auditorium, seating area, or the part where the audience sits.

So in this sentence, u gledalištu suggests in the auditorium / in the audience area.

If you wanted to say in the theater building, Croatian often uses:

• u kazalištu = in the theater

And if you mean the audience as people, you would usually say:

• publika = the audience
• gledatelji = the spectators/viewers

So:

• gledalište = place/space
• publika = people

Grammatically, gledatelj is a masculine noun.

It can refer to:

• a male spectator specifically, or
• a spectator in a general, dictionary-style way

If you want to refer specifically to a female spectator, you would usually say:

• gledateljica

So:

• gledatelj = male spectator / spectator
• gledateljica = female spectator

This is very common in Croatian with nouns for people.

Because čitati is imperfective, and that fits a neutral statement about the action of reading.

In Croatian, aspect matters a lot:

• čitati = imperfective, focuses on the process or general action
• pročitati = perfective, focuses on finishing/reading through

So:

• Gledatelj čita najavu. = The spectator reads / is reading the announcement.
• Gledatelj je pročitao najavu. = The spectator read the announcement completely / finished reading it.

In your sentence, there is no emphasis on completion, so čita is the natural choice.

A rough learner-friendly pronunciation is:

gleh-DAH-tely CHEE-tah nah-YAH-voo oo gleh-dah-LEESH-too

A few helpful sound notes:

• č sounds like ch in chocolate
• j sounds like y in yes
• u sounds like oo in food
• lj is a soft sound, somewhat like lli in million for many English speakers

So:

• čita ≈ CHEE-tah
• najavu ≈ nah-YAH-voo
• gledalištu ≈ gleh-dah-LEESH-too

That pronunciation guide is approximate, but it is good enough for a learner to start with.

Not always. Najava can mean different but related things depending on context, such as:

• announcement
• notice
• preview
• introduction
• coming-soon announcement

In a theater or event context, najava might be:

• a short announcement
• a program notice
• promotional text
• a preview of what is about to happen

So announcement is a good general translation, but the exact shade of meaning depends on the situation.