The fee is split into three parts the Base Fee which you only have to pay once, the Entry Fee for each Entry you want to submit, and the Feedback Fee for each feedback you want to receive.
Entry and Submission basically mean the same thing. For each additional entry, you can submit one more film with your music. For each additional feedback, one of your submissions will get feedback so if you have 2 entries for example and 1 feedback, one of your submissions will get feedback but the other one not.
When you later submit your film there is a box that you can check to decide if you want to receive feedback for that submission and you can also see on that page how many entries/submissions you have left and how many you can still use.
You can also always add other entries and feedback later.