This site allows HTML content. While learning all of HTML may feel intimidating, learning how to use a very small number of the most basic HTML "tags" is very easy. This table provides examples for each tag that is enabled on this site.
For more information see W3C's HTML Specifications or use your favorite search engine to find other sites that explain HTML.
Most unusual characters can be directly entered without any problems.
If you do encounter problems, try using HTML character entities. A common example looks like & for an ampersand & character. For a full list of entities see HTML's entities page. Some of the available characters include:
Lines and paragraphs are automatically recognized. The <br /> line break, <p> paragraph and </p> close paragraph tags are inserted automatically. If paragraphs are not recognized simply add a couple blank lines.