In order to put your post on the map, you need to associate location data with it.
This can be done via the edit page for each post, or can automatically be included from your email/MMS/SMS. To include location information automatically, add the following:
This is your message text, at the start of your email message. To let the system know you are including location information, add the following map="my location"
Try to make sure your location is as accurate as possible - street addresses, postcodes, etc all work. "High Street, Townsville" is better than "Townsville". Anything you can type into Google Maps and get a result for should work.
You can also include geo-tags along with your other tags, in the standard tag format:
tags="geo:lat=51.4989, geo:lon=-0.1786, other tag, etc"
If you're lucky enough to have a GPS-enabled handset that adds location information into your photos as you take them, they will be automatically placed on the map on upload.