1. You need to enable Banner Promotion on Setting section
2. The banner promotion only works on Gifts on cart. And it will show if the cart has not reach the condition. If the cart reaches the condition and customer get the gifts, it will be not showed anymore.
Example: You create a gift on cart: Buy more 3 items Get a free gift, then you can design a banner that advertise this message. If a customer buys 1 or 2 products, at cart page, the banner will show to motivate customer to buy more items.