In XenForo 2 the default style has 24 ad locations as predefined. Here is how each of them is placed in the layout of the default style.
Visual Guide
A Visual Guide To XenForo Ads
XenForo’s default style provides 19 ad locations. Here is the visual guide to how each one of them is placed.
A Visual Guide To XenForo Hooks
The complete visual guide to the position of each XenForo hook for header, footer as well as the forum_list, forum_view, thread_view and member_view pages