Google is your friend: Be nice and visit him often. He can answer questions a lot more quickly than posting them here...
A very quick search
using your subject as the search term* gave over 70,000 results:
how to use layout.cshtml as master for webform - Google Search[
^]
In future, please try to do at least basic research yourself, and not waste your time or ours.
* Only with the spelling errors corrected