If you see this post it means that BlogEngine.NET 1.3 is running and the SQL Server provider is configured correctly.
If you are using the ASP.NET Membership provider, you are set to use existing users. If you are using the default BlogEngine.NET XML provider, it is time to setup some users. Find the sign-in link located either at the bottom or top of the page depending on your current theme and click it. Now enter "admin" in both the username and password fields and click the button. You will now see an admin menu appear. It has a link to the "Users" admin page. From there you can change the username and password.
Since you are using SQL to store your posts, most information is stored there. However, if you want to store attachments or images in the blog, you will want write permissions setup on the App_Data folder.
On the Web
You can find BlogEngine.NET on the official website. Here you will find tutorials, documentation, tips and tricks and much more. The ongoing development of BlogEngine.NET can be followed at CodePlex where the daily builds will be published for anyone to download.
Good luck and happy writing.