Why does my computer keep displaying the GRUB menu when it starts up? [duplicate]

Yesterday I tried turning on my computer. It led me into this grub menu and I have no idea how to get out. I can't use my computer anymore due to this. What should I do? Do I type in a command or something?

Five keys you can press at Grub Menu

This write-up is from (omgubuntu.co.uk - Five keys to show Grub menu Ubuntu) which nicely lays out what you can do at Grub menu.

1. Shift

Ubuntu does not display the GRUB menu by default. To see GRUB during boot you need to press the right-hand Shift key during boot.

2. Up/Down Arrow Keys

When you are at the GRUB menu you can use the ↑ and ↓ arrow keys to select other operating systems and kernel configurations display in the menu. When you’ve selected the one you wish to highlight press Enter to boot it.

3. e for Edit

There may be times you need to edit a boot command,

Use the arrow keys to select a boot option and hit the e key to that entry’s boot options by hand.

You may need to do this to run a specific boot parameter, pass a kernel flag, adjust the run time level or set the frame buffer mode.

When you’re ready to boot with your modified changes press CtrlX.

4. c for Command Line Mode

Press the c key at the GRUB Menu to switch into CLI Mode. From here you can do a wealth of things, including changing menu entry names, fixing a broken install, or booting into a custom kernel configuration.

5. Esc Key

Tap the Esc key at any time to return to the main GRUB Menu screen. Should you press Esc at the editor or command line screens all configuration changes you made are discarded and you’re plonked back at the main menu interface.