Walmart Connect recently announced in-store demos and in-store audio, both in beta. Brands can already advertise on its self-checkout screens. And with almost 4,700 stories in the U.S., that's critical reach.

Ryan Mayward, senior vice president, retail media for Walmart, told CNBC: "When you think about our store, our store footprint and the percentage of Americans that we reach through our stores, we can deliver Super Bowl-sized audiences every week."

In addition, Walmart plans to install demo stations at weekends so shoppers can sample products. Consumers will be able to scan QR codes at these demo stations to learn about more shopping options.

Still, advertising is a tiny part of Walmart's total revenue.

Its global advertising business hit $2.7 billion in the most recent fiscal year, which ended in late January. That’s less than 1% of Walmart’s total annual revenue.