Google Analytics in Multi Site

I've downloaded and installed the Google Analytics plugin, but I'm a little confused as to the proper configuration. My sub sites are all set up as subdomains. I'd like to track info on each site individually, and I don't mind creating a Google account for each one.

So do I enter the tracking code for the main site and no codes for the sub sites?

Do I enter codes for each individual site?

Do I get rid of the plugin and just embed the code in each site?

What's the proper way to set this up?

Thanks!