Gist is: each box can be toggled blocked or allowed by clicking the bottom or top of the box, by type of item being blocked (css, script, cookie, media, etc, in the middle area), or for everything for the whole domain (the far left side with the site name). You can change the scope of the blocking to affect either just the site you're at or for all sites in the top left corner. There's a lock and erase button at the top to let you test changes and save them if they work.
The colors: dark green means you enabled it, light green means it was default enabled, light red means default blocked, dark red means you blocked it. It uses a bunch of host files as its default filters (you can change these), so a lot of sites will be broken by default just by virtue of them.