Zotero comes with a default list of citation styles, and you can download many more (1555 styles last time I checked) from here. Installing is simple, just click on the install button for the desired citation style.
Of course it is still possible your citation style is not included (yet). You can try your luck at the forum on citation styles, there might be somebody that already has developed the citation style your are looking for, or is willing to help you to create one. Or you can go for it and develop your own style.
The page about developing citation styles on the Zotero website isn’t exactly inviting for the novice. At least, it isn’t for me. Then I found this site, which shows the basics step by step, making it almost look… well, doable for a newbie like me. For now I am just looking how to make some small adaptations to an existing style, such as changing the number of authors that is shown before et. al is used. And yes, a clear explanation how to do this can be found on the second page 🙂
Edit: you definitely should check out this page: http://www.zotero.org/support/dev/citation_styles/style_editing_step-by-step