I don't know if I've set my PayPal account up correctly, though I think I have, and there's a box to put the donation amount in. I did read in help to set it up with a donation box. I want to have a specific amount per person. Can you explain what I need to do in order to set it up correctly?

The built-in home page Donate box is configured to allow donations of any amount. If you want to set up specific items and/or donation amounts, you'd need to go out to PayPal's site and build your donate widget there. After configuring it they will provide you some object/embed code you can simply copy and paste onto your site. Instructions for creating widgets like this are available on PayPal's site.