How to show text with clicking button in Android?

I am developing an android application as an todo list but I have problem at one part of this application.I want to create "about" part in my android app with clicking button.When the user clicks on button,a page comes and show the text to the user.

I know I have to add button on activity_main xml file but when I go to MainActivity java class,I get suffocated.I use toast but I couldn't get the what I want.

How can I do that ?