I want to allow users to register and post articles on my blog. But after posting by user, I must approve them before appearing on the website. So, Please tell me how can i start multi user blog and suggest me a good free wordpress theme for that.. Thanks.
You simply just need to go to settings, click General Settings, tick the Anyone can register box, and choose Contributor underneath. Then people can register and you have to approve them first. As for a theme any will do but pick one without too many options because not everyone knows how to use advanced features. More on it here http://codex.wordpress.org/Roles_and_Capabilities