when i am trying to use ubuntu try ubuntu option/install then after sometime its showed me that

The system is running in low graphics mode
your screen graphics card and input device sestting could not be detected corectly .You will need to configrure these yourself .

But i cant under stand that what to do now

The first thing to try is the install additional drivers. To do this, open up the Software & Updates tool from the Dash and click the Additional Drivers tab. Follow the on-screen prompts to check for, then enable, any proprietary drivers (not open source) available for your system. This is because the default (open-source) drivers for graphics cards are often not good enough, or misbehave, and you'll have a better chance with the proprietary drivers (that come from the graphics card manufacturer).

BTW, what is your graphics card?

Have you done any kind of display reconfiguring? (like dual displays, resolution, etc.) It's possible that they broke the display configuration and you should revert them to the simplest thing that works, then install proprietary drivers, and then reconfigure the display as you wish, but make sure you follow the correct method for your graphics card + proprietary driver.