I'm sure this is a very dumb question, so I apologize in advance. After about a 20+ year hiatus, I've recently gotten back into buying comics, and was looking at picking up Amazing Spider Man, and purchasing some of the back issues so I'm not completely lost moving forward. I've noticed that some of the issues have a ".1"? Like there is issue #654, and then there is a #654.1 as well?
Is that something that Amazing does a lot? Are these special issues, or do they come out at regular times? If I'm buying back issues, how would I even know there were these "sub issues"?