There's a button to the bottom right of the comment box that says "Show help." It'll show you most of what you need to know, and the rest can be found at the links there.
... but here's the summary of the main things you probably need to know: (1) links are text in square brackets immediately followed by URL in parentheses, (2) bulleted lists have stars at the start of each line and need a blank line before them.
As in Joshua Blaine's original description (below), but may be used to brag about things you've accomplished either this month (December) or the previous one (November), assuming that you haven't brought it up in any earlier Monthly Bragging Thread.