What all of the F-keys actually do?

Have you ever wondered what does actually all F-keys do? Now, let's dig deeper into it because it can turn out very useful for you in the future.
F-keys is also known as Function keys, they are used as shortcuts to proceed certain functions. Let's start with the first one:

F1
F1 is a shortcut for help function in almost all of the applications.
Windows + F1 = Microsoft’s universal Windows Help and Support.

F2
F2 is considered as an edit key. It functions as a "rename" shortcut.
Alt + Ctrl + F2 = opens the Documents Library while on MS Office suite.

F3

F3 functions as a search shortcut. (You can also use CTRL + F shortcut)

F4
ALT + F4 is used as the great escape key. It will immediately close the current program without saving.

F5
F5 is used to refresh internet browser.
ALT + F5 will do a hard refresh - it means that it will clear the browser’s cache for a specific page, forcing it to load the most recent version that includes changes to stylesheets or other scripts. It can be very helpful for web programmers.

F6
F6 is used to toggle from the desktop files to the taskbar and the system tray icons and also is used to bring focuses on the address bar on most browsers.

F7
F7 can be used to turn on Caret browsing on Mozilla Firefox.

F8
F8 lets you enter into the Windows Start Menu during the Windows boot.

F9
F9 is used in Integrated Development Environments. By pressing CTRL + F9 it will complete the code and run it.

F10
F10 shows the menu by highlighting it in most programs.
Shift + F10 = context menu (the same as the right click).

F11
F11 opens full-screen mode.
Shift + F11 adds a new sheet on applications like on MS Excel.

F12
F12 opens "Save as" function to save your work.

Which of the F-keys did you found the most useful?