Create product variations
Product variations are used if you wish to sell one product with different options, for example different sizes and colors. You might also want to set a different price for each variation
You can do this by clicking on Add variation when editing a product. Set a title, for example: Size. Click on Add variation (on the right). Set a variation title, for example: small. Set a price differentiation, for example, +20. This will make this product variation 20 (USD) more expensive than the default price. You can keep adding variations like this.