In which way you identify a Master Page and how you can bind a Content Page to a Master Page? Can a master page be nested?

Answer:

The master page is identified by @Master directive and that replaces the @Page directive which is used for ordinary .aspx or content page pages.

The MasterPageFile attribute of a content page's @Page directive is used to bind a Content Page to a Master Page.

Yes, the master pages can be nested.