Each independent domain name constitutes one level, so following an URL from the starting web site (example1.com) to a different web site (differentexample.com) will constitute a change from level 0 to level 1.
This is very useful if you are searching a web directory, for example. By setting the limit to level 1, Email Grabber will only search the directory and web sites that are just one link away.
This is also very useful if you just want to scan a single web site, not following any outbound links (set to level 0 - Starting web site only). This way, Email Grabber will only follow internal links (to the same domain name).
All URLs added manually via the Queue Manager will have level 0.
The last level limit allows you to limit the number of pages per domain name that Email Grabber scans from pages on the last level. Using this option you can prevent Email Grabber from wasting too much time on page from the last level.
Levels are also very useful when performing keyword searches.