Could anyone please help me, how to create a button and after clicking that button it have to show username and score pop-up messages which he got in the game in construct2 and how to integrate php and html in construct2?
Look in the FAQ section of the forum.
There is already a lot of topics about that:
Especially look in the section about AJAX
There is also a post about pasing things to C2 from the webpage in the general section of the FAQ:
Develop games in your browser. Powerful, performant & highly capable.
I was going to post a link to a couple tutorials, but I think they and several others are linked in the "HOW DO I" list here:
scroll down to the AJAX section, or hit control F to search the page nad type 'PHP'