Best place to learn about brand kits

Hi, and welcome! The best place to start is Adobe's own help page on creating a brand in Express — it walks through the whole setup step by step:

https://helpx.adobe.com/express/web/brands-libraries-projects/create-manage-brands/create-brand.html

In short: in Adobe Express, go to Brands in the left sidebar, click Create brand, then add your logo, colors, and fonts. Once it's set up, you can apply the brand to any design in one click, which is ideal for keeping your retail team's designs consistent.

For hands-on practice, the in-app Learn tutorials in Express are also worth a look — they cover the same workflow with examples.