Serious question: what the fuck actually happened at the end of Harry Potter

I read the books this year because I wanted to feel pain, basically, and I wanted to be justified in disliking Harry Potter. I was not disappointed. However, I still don't understand how the fuck the end of the book worked. It was so harebrained and convoluted and sloppy as fuck that I don't know what actually happened. Am I stupid or was it a bad ending? And what the fuck happened? How did they actually kill Voldemort?