problem installing Xprivacy : where is the install button?
Your device need to be rooted for Xprivacy to work, be installed properly. Even before installing it, you must install Xposed framework which requires root.

From Xprivacy Github page:


  XPrivacy is built using the Xposed framework, which it uses to tap into a vast number of carefully selected Android functions. 





  Root access is needed to install the Xposed framework.


The process is:


Root your device.
Install Xposed installer.
Install Xposed framework.
Install Xprivacy.