Please keep in mind that there is a profound difference between English and Croatian when it comes to using personal pronouns:
Personal pronouns are much less frequently used in Croatian.
The average Croatian sentence doesn't usually mention the personal pronouns, because the verb form already shows who is meant.

But, whenever the pronoun is to be emphasised, the personal pronoun is mentioned.

Synopsis: Croatian personal pronouns (nominative form)

Singular:
ja – I
ti – you
on – he
ona – she
ono – it

Plural:
mi – we
vi/Vi – you (informal / formal)
oni – they (m)
one – they (f)
ona – they (n)

Stressed and unstressed form

Personal pronouns are declined and there are two types: stressed and unstressed.

The stressed, long form can be found at the beginning of a sentence and after prepositions like a / i / ni.
💡 For example:
Njemu je pomogao učitelj – meni nije.– The teacher helped him – not me.

The unstressed, short forms count as clitics.
💡 For example:
Iznenadila ih je. – She surprised her.