Before you can submit a receipt, you need to click on the store you plan to shop. The deals available for the store will be listed. You, then, must select which offers you want to redeem. When you go to the store, buy the products you selected for that store. When you get home, you can submit your receipt. Some stores on Ibotta allow you to link your store loyalty card so you don't need to submit the receipt. However, you still need to select the items you want to buy and redeem first. I hope this info helps and welcome to Ibotta and the Community.
There are some apps (FETCH, SwagBucks, etc) that will pay you a small amount for every receipt you submit, but ibotts is not one of them.