Grub 2 multiple boot options - what do they do?

Question

I have a Lenovo laptop with pre-installed Windows 8.1 64 bit. I wanted to create dualboot (Windows + Ubuntu 16.04).

1. In Windows I disabled Fast Startup and created free partition for Ubuntu OS
2. I created Ubuntu bootable USB with Universal USB Installer
3. I installed Ubuntu 16.04 (I chose the "install alongside windows" option)
4. when the installation completed, I restarted the computer but no boot manager showed and it booted straight into Windows
5. I followed this (1st comment) process
6. in BIOS I set the UEFI boot priority before Legacy

Now when I start the laptop, the Grub menu shows up with multiple options which are:

1. Ubuntu - boots Ubuntu
2. Advanced options for Ubuntu - several options are available when I choose this: (2.1 Ubuntu, with Linux 4.4.0-38-generic, 2.2 Ubuntu, with Linux 4.4.0-38-recovery mode, 2.3 Ubuntu, with Linux 4.4.0-31-generic, 2.4 Ubuntu, with Linux 4.4.0-31-recovery mode)
3. Windows UEFI bootmgfw.efi - boots Windows
4. Windows Boot UEFI loader - boots Windows
5. EFI/Ubuntu/MokManager.efi - MokManager (?)
6. EFI/Lenovo/Boot/bootmgfw.efi - goes to Windows advanced boot options
7. Windows Boot Manager (on dev/sda2) - boots Windows
8. System setup - goes to BIOS

Several options boot Windows (3,4,7), one option (1) boots Ubuntu one option (2) leads to several "Ubuntu boot" suboptions, one (6) goes to advanced Windows boot options, one (8) goes simply to BIOS and one (5) starts MokManager.

What is the difference between all these "boot Windows/boot Ubuntu" options. And if I want to boot into Windows (or Ubuntu), what option should I choose?

P.S. I am complete Linux beginner.

Answer 1

The most important are these:

(3,4,7) are generally fine to use to boot Windows; I would stick to 3 or 4 as those boot in UEFI.

7 looks like it might be Legacy boot.

Now, for Ubuntu, use "Boot Ubuntu". The advanced options you see are simply multiple Kernels. The latest kernel will be booted. This is in place as if you install a new kernel and it breaks your system you can roll back to an older kernel.

MokManager manages owner keys and is created by Boot Repair. Ignore it.