Android Studio with Facebook (Login+Share Function)

I am a beginner who making an android app by using android studio which need Facebook login+share function.

To add a Share button add the following code snippet to your view:

ShareButton shareButton = (ShareButton)findViewById(R.id.fb_share_button);
shareButton.setShareContent(content);

I don't understand my view is in which class? Where actually should i put the code?

Thank you in advance.