If you're talking about the plaintext box that holds the code, just wrap the code in code tags? If you need specific examples for jcink you can check out this link. - In proboards, you can use the little button that looks like a C up top or you can check out here at this link.

If you want to know what you can do further, google 'bbcode' and you'll be able to do most of those things with some variations between proboards/jcink.