Can't understand how to create LVM-Luks

I know somebody already has made a tutorial on how to do this, but I don’t quite understand what is going on and how any of this works. I want to learn and understand this stuff better.

So after creating lvm partition using gparted, I then use terminal and type this sudo cryptsetup --type luks luksFormat /dev/sda2 and then I would be prompted for a password. After entering it in, then the drive is encrypted. So I then decrypted the drive again sudo cryptsetup --type luks /dev/sda2 crypt then I believe I have to then create a physical volume by typing in pvcreate /dev/mapper/crypt or something like that. I am not too sure after that what I have to do and I don’t quite understand what is going on and why I have to create a physical volume, how does it differ to a partition, and why is it that everything is going into the /dev/mapper/ directory?