Container Disk1 : Questions and Frustrations

I'm a noob at this, and I'm sure there have been hundreds of questions about this already but I have a specific issue with this 'Container Disk1' and it's been causing me problems.

Question 1: What the **** is it, and why is it there to begin with. Every time I look something up about it, get people talking about bootcamp and partitioning. I also understand that it starting being there only until after Sierra (I think). The thing is, I have never tried partitioning (as far as I'm concerned) and I have never tried installing windows on my Mac. Do either of those things affect its existence?

Question 2: Why do they have different "available space"? You may also ask me, 'Why does it matter?" So I've been attempting to install music plug-ins, one being a library of over 50 gbs. However, despite me having over 100gbs of free space, the installer claims to only have 30.8gb of free space, which appears to not be true... until I checked disk utility. So I see that my MAC HD has the 105.2 gbs of free space, while the Container Disk1 only has the 30.8 that my installer kept claiming.

Follow-up : How do 'free-up' space in the Container Disk1 then? I've tried shutting down the computer, letting the computer sit there for hours. I've had to resort to resetting and restoring my computer from a back up to finally have the space in the container down to 100gb of free space. But I don't want to have to do this every time in the future.

Any sort of help here would be so much appreciated.