The F keys or Function Keys to give them their full name do just that. They are keys that do certain functions.
F1 mainly activates a help menu in an application
F2 will rename a highlighted file
F3 generally activates a search window
F4 opens a find window
Alt + F4 closes an application
I could go on and on. Some even have different uses dependant on what application you are using eg. F12 is Save in MS Office applications.