F5 is probably the most often used function key in PowerPoint. You can quickly see how your slide show looks in full screen.
F1 is a common keyboard shortcut for all programs. This is the Help key.
The function keys or F keys as they are more commonly known, are located above the number keys on the regular keyboard.
F1 - Help
F5 - View the complete slide show
Shift + F5 - View the slide show from the current slide forward
F7 - Spellcheck
F12 - Opens Save As dialog box