Rekla sam bok i otišla.

Because the speaker is female.

In Croatian past tense, the main verb appears in a form that agrees with the subject’s gender and number.
Here, rekla and otišla are feminine singular forms.

So:

• Rekla sam bok i otišla. = said by a woman
• Rekao sam bok i otišao. = said by a man

This is one of the big differences from English: Croatian past-tense forms often show the speaker’s gender.

Sam is the auxiliary verb to be, used to form the Croatian past tense.

The pattern is:

• past participle
  • present of biti

So here:

• rekla sam = I said
• otišla = went / left, with the auxiliary understood from the first part

More examples:

• Vidjela sam. = I saw.
• Došla sam. = I came.

For I, the auxiliary is sam.

Because Croatian clitics like sam usually go in the second position in the sentence or clause.

That means the auxiliary often comes after the first stressed word or phrase, not necessarily directly before the verb the way English works.

So the neutral order is:

• Rekla sam bok.

not usually:

• Sam rekla bok.

English speakers often expect the auxiliary to come first, but Croatian clitic placement follows different rules.

Because Croatian often drops subject pronouns when they are already clear from the verb form or the context.

Here, sam already tells you the subject is I, so ja is unnecessary.

• Rekla sam bok i otišla. = normal, natural
• Ja sam rekla bok i otišla. = possible, but more emphatic

You would add ja only if you want contrast or emphasis, for example:

• Ja sam rekla bok, a ona nije.
  I said hi, but she didn’t.

Because the two verbs share the same subject and the same tense, so Croatian often uses the auxiliary only once.

Here:

• Rekla sam bok i otišla.

The second verb otišla is understood as having the same auxiliary:

• Rekla sam bok i otišla sam.

That full version is grammatical, but repeating sam is often unnecessary and can sound less smooth in a simple sentence like this.

This is the Croatian perfect (perfekt), which is the most common way to talk about completed past actions.

It is formed with:

• the auxiliary biti in the present tense
• plus the past participle

So:

• rekla sam = I said
• otišla sam = I left / went away

In English, this often corresponds to the simple past.

Bok is an informal greeting in Croatian.

Depending on context, it can mean:

• hi
• bye

In this sentence, with rekla sam bok, it means something like:

• I said hi
• or possibly I said bye, depending on the context

It is very common in everyday speech, especially in informal situations.

Because i means and, and here it simply joins two verbs with the same subject:

• Rekla sam bok i otišla.

In Croatian, you normally do not put a comma before i in a basic coordination like this.

A comma would usually appear only if there were a special pause, extra inserted information, or a more complex structure.

Because reći means to say in the sense of a single, completed utterance, which fits this sentence well.

• reći = to say, tell
• govoriti = to speak, be speaking, talk

Here the idea is:

• she said bok
• then she left

That is a short, completed action, so reći is the natural choice.

Using govoriti would change the meaning and sound unnatural here.

Yes, Croatian word order is fairly flexible, but not every option sounds equally natural.

The sentence:

• Rekla sam bok i otišla.

is the most neutral and natural version.

You may see different word orders for emphasis, contrast, or style, but beginners should learn this version first.

A good rule is:

• keep the main verb first if it is the first stressed element
• place clitics like sam in second position

So this sentence is a very good model to remember.