Shopify provides product tags as an easy way to group sets of products for a range of reasons.
This article provides a great overview of how to use tags in Shopify. You can associate products with tags either in the Shopify UI or via import files.
Seasoning uses product tags to identify a set of products which will be sold during a season. We use tags since they’re easy to set up and since you may well already be familiar with them.
If you've already defined tags in Shopify, they'll be imported into the Seasoning app and you can move onto creating the season
If not, then go ahead and set up a tag for a set of products now - this should be a set of products which will all be sold during the same time period.
You can add tags to products in the Products section of the Shopify admin UI at https://[yourdomain].myshopify.com/admin/products or alternatively in a CSV import.