Učiteljica kaže da je "trčati" glagol, a "škola" imenica.

It specifically means a female teacher.

Croatian often marks gender in profession nouns:

• učitelj = a male teacher / teacher
• učiteljica = a female teacher

So in this sentence, the speaker is talking about a woman teacher. In English, you would usually just say the teacher unless the gender matters.

Kaže means says. It is the 3rd person singular present form, because the subject učiteljica is singular.

So:

• učiteljica kaže = the teacher says
• if the subject were plural, you would get kažu = say

Da introduces a clause meaning that, and je means is.

So:

• kaže da... = says that...
• da je = that ... is

In this sentence, da je trčati glagol means that trčati is a verb.

Because the sentence is talking about the word as a verb, not using it as an action.

In Croatian, when you name a verb as a dictionary entry or grammatical item, you normally use the infinitive:

• trčati = to run

So trčati is the basic form of the verb, just like English grammar books talk about to run or run.

For the same reason: the sentence is talking about the word itself.

When Croatian names a noun as a vocabulary item, it normally uses the nominative singular, which is the dictionary form. So:

• škola = the basic form of the noun
• the sentence is classifying it as a noun, not using it in some other case

So the implied idea is škola je imenica = school is a noun.

Because Croatian often leaves out repeated words when the structure is clear.

The full version could be:

• Učiteljica kaže da je trčati glagol, a škola je imenica.

Or even more explicitly:

• Učiteljica kaže da je trčati glagol, a da je škola imenica.

But in natural speech and writing, repeating je is often unnecessary if the meaning is obvious.

It can be translated as and, but it often has a slight contrastive or balancing sense, like:

• and
• while
• whereas
• as for

Here it links two parallel statements:

• trčati is a verb
• škola is a noun

So a is very natural in this kind of side-by-side comparison.

They are in the nominative singular, the basic dictionary form.

After je in a sentence of identification or classification, Croatian commonly uses the nominative:

• To je škola.
• Trčati je glagol.
• Škola je imenica.

So glagol and imenica are not changed here because they are predicate nouns saying what something is.

Because Croatian has no articles.

That means a word like učiteljica can mean:

• a teacher
• the teacher

The exact meaning depends on context. English requires an article, but Croatian usually does not.

Croatian word order is more flexible than English word order, but short unstressed words like je follow special placement rules.

After da, the natural order is:

• da je...

So:

• da je trčati glagol = natural
• da trčati je glagol = unnatural

A good beginner rule is: when you see da je, keep that pair together.

Because the sentence is talking about the words themselves, not using them in their normal meanings.

This is called mentioning a word rather than using it. In English, you do the same thing when you say something like:

• Run is a verb.
• School is a noun.

In textbooks, this can be shown with quotation marks, italics, or bold.

Useful sound rules here are:

• š = sh as in shoe
• č = ch as in church
• c = ts as in cats
• lj is a single soft sound, roughly like the lli in million

So approximately:

• škola = SHKO-la
• trčati = tr-CHA-ti
• učiteljica = u-chi-TE-lyi-tsa

The exact pronunciation depends on accent, but those approximations are good enough to get started.