Amazon refunds, How do they work?

Hey, I am new to the online world more or less, and i wanted to know how the amazon refund works, i mean step by step, can anyone who have done it explain it to me?
What i most want to know is do i buy it, then i use someone's services to refund it after a few days, or after it shipped? or when it arrives to my house?

Thanks in advance!

I don't know where this post should be so i posted on general, sorry in advance if i shouldn't post this here, and sorry for my english