SIMPLE paypal donation

[eluser]ztoby[/eluser]
greetings

sorry for posting a frequent topic, but after many many many many hours of googling i'm really confused.

I just want to integrate a simple paypal donation - NOT buying items - and i can't seem to find where to start from.

what i want is a form with the amount the user donates
then he is taken to paypal to pay
and then back to website for a thnx page

so, is codeigniter-paypal-ipn needed? is it used to send the user to paypal or just after the user comes back? can i use a sandbox paypal account to test the donation process

sorry again if the question is dumb but i'm new to codeigniter
any help would be really appreciated
zto