“Deep web” and “dark web” are not the same thing. My students’ grades, for instance, are part of the deep web: Some random person with Internet access can’t access them. But with the right password, I can, and I can do it through a perfectly ordinary web browser. Likewise, my Gmail messages, my bank statements, the moderator tools here, etc. There’s a lot of Deep Web out there.
The “dark web” is things that are kept not only private, but hidden, usually because they’re illegal, and they usually do require special software like tor to access.