Creating submixes on a 12 channel Mixer

Hi All.  Me again.   I have an embarrassing question....thats because I have been recording on a 16 track multitrack recorder ( BOSS BR1600) for many years, but I have never used an outside mixer or created sub mixes....I've never had a need for it until now.

I recently purchased a Mackie ProFX12, 12 channel mixer.   6 Pre-amped XLR inputs. 4 stereo channels with 1/4" inputs.

My goal at this point is to create a sub mix for drums. After I better understand how to do this, I will move on to other instruments or backing vocals, etc.  The main reason is to free up tracks on my 16 track recorder, which currently only has 8 simultaneous inputs with 16 track playback.

I want to run 4 mics or more to the drums: 1 kick, 1 snare, 2 overheads....maybe even add 2 toms...depends.

I want to be able to tweak and adjust the EQ's for the kick and snare by themselves individuallly.  The 2 overheads I want to have together on 1 track.

Guys, I don't how to group instruments into sub groups.  I mean, I see why it works and the benefits , but not having done this I'm a little lost.

I read about "assigning" groups and "routing" channels to buses, etc, but every link I find only describes the benefits of doing it.   I just don't know the actual steps to take.

Thank you in advance.

S.