In the Product category of Shop tools, there is an option to set up a Brand filter for the visitor side of your website allowing a visitor to limit the displayed results to a particular brand. The Brand filter is a separate tool from the attribute setttings of a product. It's optional and it appears on a category page of products when enabled.

The first step in setting it up is to add all the brands you carry to the Brands tool in the Product tools in the Shop application.(Shop --> Products --> Brands)

Next, edit each product and select it's appropriate brand from the Brand dropdown the Product Info tab of the product. (Shop --> Products --> click/search on the product)  If the Brand does not appear in the dropdown, then it isn't active in the Brand tool.

The last step is to activate the brand filter option on any shop category that you want it to appear. (Shop --> Products --> Categories --> Click on the Category --> set Enable Price Filter radio button to Yes. )