Basic formatting:

Make text bolder: [b]text[/b]

Alternative: <b>text</b>

Make text italicized: [i]text[/i]

Alternative: <i>text</i>

Make text underlined: [u]text[/u]

Alternative: <u>text</u>

To quote text: [quote]text[/quote]

Alternative: <blockquote>text</blockquote>

Make text point to webpage or image: [url=http://www.website.com]text[/url]

Alternative: <a href="http://www.website.com">text</a>

Display html code: [code]html code[/code]

Note: The alternatives are HTML codes and will work at any site where basic HTML formatting is allowed in the comments.  The simpler codes will work at many sites, too.

Posting images:

You could post the url of an image on a separate line, and this should often work.  However, some sites do not allow their images to be displayed at other sites, and even if they do, the site owners incur the bandwidth charge for having it displayed outside the site.  Therefore, upload your image to a site like imageshack.us and post the url of the image they provide to you, preferably the url of the thumbnail of the image if it is large.

Spell check:

Many browser toolbars offer a spell check functionality, but these toolbars are not recommended because they typically record the pages one visits.  A better alternative is to use the latest version of the firefox browser, which has a built-in spell checker that operates by default.  One could also type a comment in a wordprocessor and let it correct the spelling, then copy, paste, preview and submit it.

Final check:

Click on the preview button to see that everything is as you would like it to be and then click on the submit button.