The best way to create a map is by going to Create->Map [Take me there] menu item on the right hand side. You should see an interactive map which you can pan, zoom etc. Every time you click on a location on the map, the site will insert a marker for you. Once you are happy with your map and markers, copy the code that appears near the bottom of the page. It should look something like
Now proceed to the place you want to have this map on. It can be a blog post, comment, forum entry, story etc. Just paste this code you just copied into the text area. Make sure that you are not using rich text editor and are using 'Filtered HTML' as input format. You should be able to see these options below the text box where you are typing. Write the remainder of your text as usual keeping the Input format as Filtered HTML and press Preview and submit. You are done! Its as easy as that.
Note that currently the functionality for Lines and Circles is limited due to the development state of software we use to run this site. We are working on getting them right, but the solution depends on factors beyond our direct control.