Before you set up different prices per season, make sure you have read this article about how to set up seasons in your Bookinglayer account.
This is an example of how your seasons should look like after you set them up:
Please note you can select different date ranges and titles for your seasons
After having your seasons entered in the system, go to your inventory module and create a new product (accommodation, service, package, etc...). When you set the pricing of this product you will be able to select a "Per Season" pricing.
After you save your changes, you will be directed to the product's setting page. On the left side menu, click on Pricing (1) and set up your pricing structure according to the seasons you have entered before (3).