Stereo & surround mixes in same project?

I’m a bit confused what you meant here. What’s the difference between Groups and Stems. I thought your groups are the stems? So you have a group for dialog, a group for SFX, a group for music. Aren’t that simultaneously your stems? Or could you elaborate a bit on this setup, how this would look? What am I not getting?

Also, you can route a group only to one target, how do you route a stem to 5.1 AND stereo? One direct routing, one send?

thx
Chris