How do I integrate with my site?

There are several ways of doing it – it all depends on what the desired end-result is 🙂
1. First of all – you will have to change that “main page” to have .php extension.
2. You can use a feedreader (search) and display the RSS feeds of your blog on your main page
3. You can use the Loop in your main page:
http://codex.wordpress.org/The_Loop
4. You can create a theme that looks like your design:
http://codex.wordpress.org/Blog_Design_and_Layout
5. You can try something like in this guide:
http://www.transycan.net/blogtest/2005/07/05/integrate/