It's no secret that Horace Slughorn gave Voldemort information on making horcruxes, and a major thrust in the sixth book is Harry and Dumbledore trying to find out what Slughorn told him.
With that said, it seems like Voldemort already had a fair bit of information about horcruxes when he went to Slughorn. I'm slightly confused as to how the information Slughorn gave him actually helped him - it's not like Slughorn gave him an article on "how to make a Horcrux in 10 easy steps," and the majority of the things they discussed he already knew. And Slughorn never really answered Voldemort's question about how many horcruxes it's possible to make. That being said, how did Slughorn's information actually help Voldemort, and how was it enough information for him to actually make one?