Move to the "Provide amounts" tab and enter the kilos or grams of the different feeds you want to use. The screen is empty until you enter your amounts. You can enter amounts directly into the table, or change the allocation of individual feeds by using the arrow buttons.
PC-Horse shows a limited graphic representation of how well the nutrients in the ration will cover the requirements of the horse. You should adjust the allocation of feeds in order to achieve nearly 100% coverage of the requirements for energy and indicated nutrients. If you have difficulties with formulating a balanced diet, you should go back to the "Select feed" page, and select suitable feeds.