Let's say you want to buy a printer from a retailer. The retailer also sells replacement ink cartridges, and so does the printer manufacturer. The manufacturer prefers that you buy the ink cartridges directly from them, because their margins are higher when they don't have to pay the retailer a cut.
To encourage customers to buy the cartridges directly from them, the manufacturer provides a link or QR code to their online ink cartridge store on the product box, printer manual, and another paper insert inside the box. The manufacturer might offer more competitive pricing than the retailer or some other enticement, like a coupon.
However, the retailer implements an anti-steering rule, preventing the printer manufacturer from providing a link or QR code to their online ink cartridge store on the product packaging, printer manual, or anything inside the box, as a requirement for the printer to appear on the retailer's shelves. (As a result of corporate consolidation, there is only one other retailer in the entire country.) This is the equivalent of what Apple is doing to apps in their App Store: preventing developers from disclosing that users can purchase subscriptions or other app-related digital goods on the developer's website.