It’s been a very long time for me.
To get into St Peter’s square we just walked in.
The Basilica, the Vatican museums I remember had lines. The papal audience was for ticketed participants. My school at the time arranged that.
I’m still kicking myself that I missed the Sistine Chapel part of my trip. I overslept and missed the tour bus. And the fountain of trevi was being restored , so I couldn’t throw a coin in to ensure my return.