Once you are set up as a contributor, you can easily email in a post by sending an email to firstname.lastname@example.org.
The subject line of your email will be the post title, the body of your email will be the post.
You can add tags by entering them in the subject line: ((tags: AMS, social media))
Strip out your signature by ending your post with #end.
Here's the Posterous help page about emailing tips - http://posterous.com/help/email_tips
If you prefer to use html when you post, either in your email or on the web, use Markdown. It's techy so here's more info:
Here's the Posterous help page about html markdown - http://posterous.com/help/markdown
The Posterous FAQ page has info on what happens when you post any of a whole list of media - images, sound files, video, etc. http://posterous.com/faq. Our favorite? If you include a YouTube video link, it will automatically post the actual video.
Please experiment! We wouldn't be techy if we didn't enjoy playing around... :)