In XenForo, templates can contain HTML or CSS code along with a wide range of template Syntax like if conditions, foreach syntax, contentcheck etc.
The Admin control panel or commonly termed as admin cp is the admin area of a XenForo forum which can be accessed via a web browser.
If you have lost access to email, there are many ways to reset the password using phpMyAdmin. Here are a couple of really simple ways to reset it.
Usergroups in XenForo has permission set only for the front end (inline moderation, edit post, ban users etc) and provides no access to the admin area.