I need to know what the keys f1-f12 keys usage.

The uses for the function (f1-f12) keys varies based on which program you have open at the time. Different programs use them for different things.

However, your computer also has some default uses for these keys when combined with pressing the fn (function) key.

fn + f1 locks computer

fn + f2 changes our power use profile

fn + f3 puts the computer to sleep

fn + f4 puts the computer into hibernation mode

fn + f5 changes the display/output mode

fn + f6 decreases the screen brightness

fn + f7 increases the screen brightness

fn + f8 enables/disables wireless connections

fn + f9 enables/disables the touch pad

fn + f10 turns the cursor overlay on/off

fn + f11 turns the numeric overlay on/off

fn + f12 turns scroll lock on/off

Most of the time, F1-F12 will have specific associations with the operating system that is installed on the machine as well as the BIOS and any other software installed. For that model in particular, the user manual states several different uses for those keys. The best way to see what the keys do is to download the user's manual here and go to page 193. There, you will find detailed instructions on what each key does. When the machine is starting up, if you hold F2 or F10, this usually brings up the BIOS setup; if you hold F8, this will allow you to boot the machine in safe mode; and holding F12 will allow to change the boot device priority.

Hello there,
Here is a detailed answer on what commonly the "Function" key are used for. http://www.computerhope.com/issues/ch000306.htm
On your laptop, if your function keys have a small symbol below the text, these are additional functions of the keys. There will be a key on your keyboard labeled Fn. If you hold down the Fn key, and press one of these symbols, then your computer will perform that function. These functions should be in your manual, and they are intuitive too. They range from increasing and decreasing sound and brightness, putting your computer to sleep, locking your computer, changing displays, etc.
I hope this has helped. Thumbs up are much appreciated!

These keys have various settings depending on what programs you are running, but used in conjunction with the fn key, they switch on and off various parts of the laptop, eg on my acer they are

FN+
F1 Help menu
F2 +F3 not sure lol
F4 sleep
F5 switch screen (if you ahve an additional screen connected
F6 show on both screens as above
F7 touchpad on/off
F8 Mute on/off
F9 nothing
F10 nothing
F11 Number lock (converts some keys to use like a numberpad
F12 Scroll lock

Hope this was helpful