I needed to do some hard drive management for a friend's computer and it had a UEFI boot partition. In order to accomplish what I was after, I really needed to understand the UEFI boot process and this article helped tremendously.
UEFI boot: how does that actually work, then?
Here are some additional UEFI resources:
Ensure the correct EFI boot entries are created after switching from CentOS to Oracle Linux #70
Use Linux efibootmgr Command to Manage UEFI Boot Menu