A loud voice boomed that proclaimed that Jesus has been glorified and will be glorified. Turns out that other people heard that voice. But Jesus said that the voice came for the sake of the other people who were wondering about the voice (12:30). In other words, other people can know that Jesus has been glorified and will be glorified.
Jesus then said that now is the time of judgment of this world and that the ruler of this world will be cast out (12:31). Jesus is referring to how the world will judge Jesus (on a cross), and he knows the event would happen likely from the attitudes of the people who want to capture Jesus. On the cross, Jesus would also cast out the ruler of this world (known as the devil as stated from 1 John 5:19), which is a reference to how the cross is the beginning of the end to the devil (AKA the ultimate bad guy).
Afterward, Jesus stated that if he is "lifted up from the earth", he will "draw all people to [Himself]" (12:32). The lifting up from the earth is a reference to the resurrection that would happen after the death on the cross to demonstrate Jesus's power over death. Additionally, the drawing of people talks about how Jesus would guide every single person to Himself (though people would ultimately choose whether or not to accept Jesus or not). Jesus not only provides the path for everlasting life (via death/resurrection where Jesus demonstrates his power over death) but also helps everyone learn about Him.