Learn Croatian: Nisam umoran jer često spavam. - I am not tired because I sleep often.

Spavati (to sleep) is a regular verb ending in -ati. To make the present tense for "I", you drop the -ti from the dictionary form to get the base (spava-), and then add the "I" ending -m. This gives us spavam (I sleep).

If a woman is speaking, does the word umoran change?

Yes! Umoran is the masculine form of the adjective for "tired", meaning the speaker here is male. If a woman is saying this sentence, she would say Nisam umorna by adding the feminine ending -a.

Is nisam one word or a combination of words?

It is written as one word, but it is a combination. In Croatian, to say "I am not", you attach the negative word ne to the short form of the verb "to be" (sam). The e drops out, combining them into the single word nisam.

Why aren't we saying "Ja nisam umoran jer ja često spavam"?

In Croatian, you usually leave out the pronoun (like ja for "I") because the verb ending already tells you who is acting. Both nisam (I am not) and spavam (I sleep) are specifically in the "I" form, so adding ja is only done for strong emphasis.