It works in much the same way that the RTF posting option does and more, and it comes with the added bonus of not being evil like the RTF posting option is.
You can get it here.
How to post
If using the LJ posting interface, the best way to post is using the HTML option. I know coding can be confusing and annoying and the RTF option is easier, but the RTF posting option is made of pure evil...I may have already mentioned that.
For your convenience there is a handy posting template located in the side bar of _starcandy, the post is here. Copy/paste the code inside the box in that post into the HTML posting option.
Then type in the rest of your header information:
Then that's it, you're done. Hit the post button and then you are ready to tag.
If you absolutely have to use the RTF posting option then it's best to start completely over if you are going to cross post your fic to other communities. When a comm has a rule about not changing the default text (Like this one soon will) and the mods yell at you for changing the default text (like we soon will be) and you have no idea what you actually did to change the default text...well RTF is the culprit. Copy/pasting what you have already posted to your journal will result in YOUR journal layout settings being copied along with it. Those settings will override the settings of the comm you are posting to and voila the default text has been changed and the mods will yell at you and you didn't even do anything. See, RTF is evil.
The best thing to do is start over and completely type out your post again before posting it to any community.
How to tag
After you have posted, click the little icon to edit tags to your entry.
Then select the tags you wish to apply to your fic.
Hit save changes and then it's all done. Go back to your entry and it should look like this:
The tags are set up so that only the author of a post (and the mods and maintainers) can tag a post. If you tag incorrectly then grab a mod and tell them because you will not be able to remove the incorrect tags so the mods will have to do it. We're all listed in the user info, just pick one and PM or email, we don't bite and are happy to help.