With selling dreams they mean selling the scene in which your insecurity has been relieved.

People feel pinned down in their life, so a common dream sold is to be free. Think of Mac and their proposition of enabling your creativity (a creative person is unconstrained). A lot of car and motorbike companies also show their products as liberating in different ways.

Beer ads often show popularity and unselfconscious social interaction, which is a big deal for young guys.

For course there's dreams of beauty, success, feeling accepted.