How does one access the dark web?

I promise I’m not asking for criminal purposes. I read a lot of fiction and I frequently see characters using the dark web to help them with something. I’m not super computer savvy, so I probably couldn’t access it if I wanted to. I’m just curious how it all works.

Dated movies make it look like you have to use old DOS-like programs and strings of code to “unlock” the door to enter the dark web, but I doubt that accurate.

Is the dark web a separate entity from the “regular” web? Or is it more of legit or seemingly legit websites eventually get corrupted and repurposed so they can be used as a cover for nefarious activities?

Explain to me like I’m a mature 10 years old 😅