The Undo is done by pressing Ctrl - Z.
Use the Undo command. You can do it in the menu or by pressing the undo icon or pressing the Ctrl - Z key combination.
F12 is a developer key. Pressing on on most browsers allow the user to see the development code. They can't edit anything, so no, it is not used for "hacking". Hacking is highly illegal, so no computer is going to come pre-equipped with hacking capabilities.
in Windows Software Applications CTRL+Z is mostly used to UNDO.
Print Screen by pressing key PrtSc just after F12 and before Pause Break. Then paste that image into paint (for example) and edit to your pleasing.
Undo is Ctrl-Z. Redo is either Ctrl-Y or in some programs Ctrl-Alt-Z.
Pressing and holding the Ctrl key and then pressing the Z key will undo the last action taken, and could retrieve a formula that you have lost. If you hit Ctrl and Z several times it will keep undoing the previous actions, so you can undo more than one action if you need to.
There are different ways of saving in Excel. You can go to the File menu or Office button and pick Save. You can use Save As if it is the first time it is being saved. You can use the Ctrl - S key combination. Pressing F12 opens the Save As dialog box. Shift F12 will save a file.
If it is something you have just done, then you can retrieve it by hitting the Undo icon, or picking it from the Edit menu or pressing and holding the Ctrl key and then pressing the Z key.
F12 will do a Save As in Microsoft Word. In combination with other keys, it can do other things: Shift-F12 will do a Save. Ctrl-Shift-F12 will print the document.
The answer largely depends on what make of computer you have, as different manufacturers use different options. That said try pressing the F2, F10, F12, or the delete key continuously as soon as you power up you PC until you see a message indicating that the bios is starting or the bios screen appears. WARNING: be careful when changing settings. Always make a note of what changes were made in case you need to undo anything.
F1-F12 are often used to quickly access a part of a program, such as F12 opening developer tools in Internet Explorer.