Firewall - Need advice re: ODS agent

Can anyone suggest where I might find information to help me learn about my firewall (I have read through the help from Network Preferences but I need a basic understand of the terms and how to read the logs - I'm concerned because until now I've had my firewall settings on both my imac and macbook set to Allow all incoming connections. I just checked my security preference on my imac and while it still is on "Allow all incoming connections", it has ODS Agent in the box. Not sure what that means and how that got there-- it is not like that on my macbook. Obviously I need to start from scratch and learn the basics to understand how to set it up. Also,some preference settings seem different and my imac has been slow so I'm worried and not sure where to start to understand what to do so I hoping to find a tutorial or something. Thanks. Ellen