I am having problems in tuning pid's of my quadx, as i am new to this i m having only basic knowledge of p,i,d.
And cant figure out the best values to make my quad fly. I m tuning using the "Ez gui ground station" android app to change the values,should i use Multwii Gui confg. instead?

What board are you using?

Arduino uno board with Multiwii 2.40

I have just seen the user interface of Multiwii once. It seemed a bit difficult to understand. Are you using modules such as MPU 6050 etc along with the UNO? Better get a board which can be configured using mission planner, betaflight or librepilot. Get an APM board or a Pix Hawk (costly cousin of apm) instead of investing your time on comparatively basic Arduino Uno board if Arduino based board is a necessity. Default PID / gain values which come along with the firmwares are enough to give you a pretty clean flight, you can use the auto tune flight mode in APM if tuning is necessary. happy flying.

you may find a good video on PIDs in this play list. : https://www.youtube.com/user/Painless360/playlists