The title makes it sound complicated, fortunately it's not!
If you'd like to segment your email sends, this has has always been possible with Mitingu. Multi-level filters just allow you to segment even further.
For example. I want to send to all my contacts that have the tag "marketing" but not those that also have the "sales" tag.
Here's how we do this...
1. Go to your event menu, select Communications and then choose Add Scheduled Email
2. Enter your email details and then begin segmenting your send by first choosing which range of contacts it is going to
3. Then choose your first range of tags - With Any, With All, Without
4. To add another layer to your filter, select add new rule and then add your additional rule - With All, With Any, Without
Once you've done that, click Schedule Email and your email send will be scheduled to send with the filters applied. The above example would be sending to all contacts tagged "foundry", excluding those that were also tagged "foundry-invited".