Learn Croatian: Nema na čemu, to je moj posao. - You're welcome, that is my job.

It literally translates to "There is not on what" or "There is nothing on which [to thank me]". Nema means "there is not", na means "on", and čemu is a form of the word for "what" (što). Croatian uses this phrase exactly how English uses "You're welcome" or "Don't mention it".

Why does the word nema mean "there is no"? I thought it meant "he, she, or it doesn't have".

You are right that nema is the negative form of ima (he/she/it has). However, in Croatian, ima is also frequently used to say "there is" or "there are". Therefore, its negative form nema translates to "there is no" or "there isn't any".

Why do we use to (neuter) here instead of a masculine or feminine word for "that"?

When you are referring to a general concept, a situation, or an entire previous statement rather than a specific physical object with a known gender, Croatian defaults to the neuter pronoun to. Here, "that" refers to the general act of doing a favor.

Why is moj posao masculine if posao ends in an "o"? Don't nouns ending in "o" usually mean they are neuter?