Tube Newbie question

I'm trying to learn more about tube pre-amps. I'm overwhelmed with the codes and test numbers for vintage tubes. Can anyone give me a simple explanation of what to look for in a tube? Does anyone know any good learning resources for this technology?

I've read in forums about people saying, for example, the 'Amperex USA made 6922', made their pre-amp sing. These are old tubes. Don't they wear out?

Thanks so much!!