The Suggested Amounts section allows you to choose what you would like for the three donation buttons on your form. For a Registration form, you will likely want to hide the buttons and only provide the manual entry for a donation.
If you haven't read the Registration Design article, you will want to start there for all of the things to consider creating your Registration form.
Section Heading: The Section Heading can be changed or left blank if you do not want a section break to show. If you want to add some text or an image with your Registration, you may leave this title/Heading blank, so the added elements can flow through different sections.
Otherwise, you will likely want it to better describe what this is for, such as "Consider adding a donation when you register"
Show/Hide Switch: Usually you will want to change this to Hide. While offering the option for a donation may be beneficial, having the large buttons here takes away from the main function of the Registration form: RSVPing.
Donation Button Amounts: Since you are most likely not using these buttons, you can ignore them. Otherwise, put in the levels of donations you want from your registrants.
Default Donation Amount: Since the buttons are not being used, the Default Donation Amount should be an amount to suggest to your registrants, if they would like to add a contribution above and beyond their sponsorship level. More than likely, you would want to change this to $0.00. It is a suggestion to donate, not a requirement, so having an amount already selected may confuse and push away your registrants.
If you wish to further personalize the section you can Add Form Elements, such as adding a text, image or video or select different initiatives or anything else.