It’s a vpn client on steroids that creates a VPN network (based on your provider) which you can then use to run docker containers inside of, as well as create http & shadowsocks proxies for your VPN network etc.

Comments inside the docker-compose.yml files?

Backblaze b2, borgbase.com. There are also programs like dejadup that will let you backup to popular cloud drives. The alternatives are limitless.