In order to enter the donation form for one or more products of your shop, go to plugin option panel and click on the tab “Products & Donations”.
Click on “Add products” andy you’ll see a screen like this one, where you can enter product name:
If you enable the option “Set donation as compulsory” you can choose to make a donation compulsory for download/purchase of the related product. Users cannot add the product to the cart unless they make a donation (in case you had set a minimum and maximum value, the donation has to be of an amount belonging to that range).
N.B. If the donation has been set as compulsory, its removal from cart removes also the associated product from cart. In such cases, in fact, product and donation are bound to each other and the the order is complete only if both of them have been added.