It's not a dumb question, everyone asks it at some point or another
If you are not already logged in, go to http://www.3fatchicks.com/diet-blogs...3/wp-login.php
and log into your admin panel.
You'll see a link in the upper left area to write a new post or a new page. Choose to write a post because that appears on your blog front page and can also go into categories if you create them. A 'page' is something like an 'about me' page that is static.
I can't give you specifics because I no longer have access to the blogs and it uses a different version of Wordpress than I use elsewhere. However, that should get you started. If you log in and can't find the option to write, please let us know.