Još sam nesigurna.

Croatian often leaves out subject pronouns when the verb already makes the subject clear.

Here, sam tells you it is 1st person singular: I am.

So:

• Još sam nesigurna.
• Ja sam još nesigurna.

can both mean the same thing, but ja is usually added only for emphasis, contrast, or clarity.

Sam is the present-tense 1st person singular form of biti (to be).

So:

• sam = am

In this sentence, it links the speaker to the adjective nesigurna, just like am does in English:

• I am unsure

Because sam is a clitic in Croatian. Clitics are short unstressed words that usually go in the second position of the sentence or clause.

So in:

• Još sam nesigurna.

još comes first, and sam takes its usual second-position spot.

This is a very common pattern in Croatian word order.

Here još means still.

It often has other meanings in other contexts, such as more, another, or yet, but in this sentence it means that the state continues:

• still unsure
• still uncertain

Nesigurna is an adjective.

It comes from:

• sigurna = sure, secure
• ne- = a negative prefix, like un- or not

So nesigurna literally means something like:

• unsure
• insecure
• uncertain

Which English translation fits best depends on the context.

Because it agrees with the speaker in gender and number.

In this sentence, the speaker is understood to be:

• feminine
• singular

So the adjective is nesigurna.

If the speaker were male, it would be:

• Još sam nesiguran.

This is a very important feature of Croatian: adjectives often change form to match the person or thing they describe.

Yes. The form nesigurna tells you the speaker is female.

Even though ja is omitted, the adjective gives that information away.

Compare:

• Još sam nesigurna. = said by a woman
• Još sam nesiguran. = said by a man

They are close, but not always identical in tone.

• Još nisam sigurna = I’m still not sure
• Još sam nesigurna = I’m still unsure / uncertain / insecure

Very often, for the exact English idea I’m still not sure, Croatian speakers may prefer:

• Još nisam sigurna.

The version with nesigurna can sound a bit more like a lasting quality or state of uncertainty, and in some contexts it can also mean insecure, not just not sure.

Yes. That is one reason learners may hesitate with this word.

Depending on context, nesigurna can mean:

• unsure
• uncertain
• insecure

For example:

• if someone is deciding something, it may mean unsure
• if someone lacks confidence, it may mean insecure

So context is very important.

Yes, you can.

Adding ja is possible, but it usually adds emphasis:

• Ja sam još nesigurna, ali ti si već odlučio.

Without ja, the sentence sounds more neutral and natural in many everyday situations:

• Još sam nesigurna.

Yes. After biti (to be), predicate adjectives like this are normally in the nominative.

So:

• ja sam nesigurna
• ona je sigurna
• oni su nesigurni

The adjective agrees with the subject and stays in the nominative form here.