Configurable products are nothing new, it’s just a collection of simple products. Difference between the configurable and simple product is that configurable products are a single product with a number of variations like size, colour, etc. For example: You are going to sell a t-shirt but with 3 different sizes called Small, Medium and Large in two different colours called red and white. So to sell such products easily, you can simply use Configurable products that allow your customers to select the correct size and required colour.
How to Add Configurable Product in Magento 2