fragment issue (out of course content)

[AbdelrahmanHamoda]

I have an app , I tried to apply what I learned recently , I already created and displayed a fragment in my main activity , my issue as following :
I have implemented Button in my fragment layout
I want to make use of this button to close fragment ,
I already tried to use interface to establish the communication between fragment and its host activity , But an error raised , and I don't know why , anyone can help please ?