Search and map pages
Create a page, then pick MLS Genie — Search Results or MLS Genie — Map Search from the Template dropdown in the page editor. Search results are contained by default and map search runs full width, because a map in a reading-width column is a map nobody uses.
Page width
Each page carries its own width choice — contained, full width, or the template default — set from the MLS Genie Page Width box in the page editor. Only the MLS section is affected; everything above and below it keeps whatever width your theme gives it.
Listing pages
There is nothing to assign, and you are not locked in either. Under Page Templates settings, Listing pages offers three choices: Automatic uses the MLS Genie listing page only where your theme has no property layout of its own, so a template you paid a designer for is never overridden; Always uses ours regardless; Never leaves listing pages entirely to your theme. Automatic is the default.