Then I went to Superdrug, a famous beauty shop in Britain. Many products are on sale, such as "buy one get one free shampoo" and "buy three get two free skin care products".

Buy three get two free means to buy three kinds of goods at the price of two kinds of goods.

Mix and match ... means you can match any kind of goods.

If you don't understand, ask again. I hope to adopt it in time. Thank you!