Create a new user role

I'm looking for a way to create a new user role where I can control what pages a user is specifically able to edit. The site listed above is a "ghost" site for testing purposes, but the main site is for a non-profit and I need to be able to give each individual director the ability to update their specific page, but not others. I thought at one point I had the ability to add user roles (aside from standard: Administrator, Author, Editor etc) but I can't find it anymore.

I would specifically love to be able to turn off every single page on the backend except the ones that person should be able to see and edit.

I should add that while I'm pretty confident with Wordpress, I really don't know anything about CSS so if I need to add a code or something it would be useful if you could write it out for me to copy/paste.