Categories and sub-categories are available to group products together on Lemonstand, but not on Shopify, which uses collections in lieu of categories.
You would use Lemonstand Categories the same way you would Shopify Collections, and vice-versa.
Lemonstand has collections also, but they are used differently. Read more about collections.
Lemonstand is the winner for me. I like the way they let you group items into categories and sub-categories as opposed to collections and tags on Shopify. However, both methods technically get the job done.