i am holding the FN key and done everything but my brightness keys r still not working also there is no option of brightness i

You will probably have to go to the manufacturer's website to find an appropriate driver for that issue. But I am pretty sure it is a built in function by default, but I could be wrong. Does the FN key work with other keys? If not then it could be that key has malfunctioned.

For now you can go to the Control Panel, click on Hardware and Sound, then under the Power Options section you need to click "Change power-saving settings". Click the "Change plan settings" for the profile you are currently using and from there you should see a slide bar to change the brightness of the LCD panel.

Laptops generally have a battery icon in the Windows Tray, bottom right. There should be a boxed arrow icon that you can click to show all hidden icons. In there should be a battery icon. When you right click the battery icon you should see an option to change the power settings. This is faster than going through the Control Panel.