Welcome to posting. Basically, formatting on the web uses a type of programming called Hyper-Text Markup Language (HTML). It is very easy and can be practiced in the FreeRepublic
HTML Sandbox where you can learn to format text, post links, and insert pictures.
To answer your specific question, put a "<i>" in front of the text you want italicized and a "</i>" after it. Also, insert a <p> for new paraghraphs and a <br> for line breaks.