Filter runs based on tags, you need to modify the products first to make your filter work.

Step 1: From the Shopify Admin page > Products > pick a product.

Step 2: Scroll down and find the Tags section, add necessary ones for each product (size: S, M, L,... or color: white, red, etc.)

  • For example: If I add Red and tag for this item, it will show up as a result when the filter runs.

Step 3: Go to sidebar settings, write down all needed tags for filter selection and separate them by commas. 

Step 4: Filter check.