I think you've got the idea now, but basically it varies. Some characters find random modern computers that just work for some reason, some use magic books and such, some (Indiana Jones for example) connect via the closest thing that would exist in their setting. I think there are some characters where the mun just handwaves the issue away entirely--I know I've never addressed what Eve uses, for example, although in her case it's plausible she just has an Internet connection in her head.