Harry spoke the word "open" in Parseltongue, causing the locket to spring open. Inside the locket's picture windows were two eyes that resembled Tom Riddle's eyes, before his soul-severing caused his eyes to turn red.

Who did Tom Riddle get the locket from?

Discovered in chapter 20, Lord Voldemort's Request

The locket was in the possession of Hepzibah Smith, who purchased it from Borgin and Burkes for an extortionate amount. It was shown to Tom Riddle during a visit to Hepzibah. The locket was found to be missing after Hepzibah was murdered.

What did Ron see in the locket?

Encased in the locket, Voldemort's soul fragment had been eating away at his mind, whispering terrible thoughts that he couldn't dismiss. As much as Mrs Weasley loved each of her children equally, Ron couldn't help but feel insignificant.