Simple product options (simple variations).
User can create a simple options called something like "Size", and add values to it like XL, L, S, etc. These can then be chosen in the frontend, on products, and will be shown in cart etc.
Each value can also have a price defined which gets added on top of the product price.
composer require nobrainerweb/silvershop-simple-options
This module was inspired by Magento's product options functionality
Its much easier to create these instead of variations (UI wise). Variations have their place, but might be too complex for some clients.
This form of variations on a product does require the shop owner to handle any combination of options that actually dont exist in real life.
You can not use both Variations and simple options at the same time, on a product