What exactly is a multisite and will this work for my websites?

We have been using WPTwin to clone our websites and i just saw this multisite thing with the super admin which could save us a lot of time instead of having to clone each website individually.

So how exactly does this multisite thing work?

We have a number of websites that have the same theme but they go to different domain names for our clients. So the only difference between the websites are basically the contact pages with the clients specific contact info and little stuff like that on the websites.

So will this multisite work for our websites?

And also since this multisite has a super admin, does that mean if we make a change on the main website then that change will happen to all of the other websites under the main multisite?

Example: If the WordPress theme has a slider with different images and we went to the main website (under the super admin) to change the images, then would those images change on the other multisite websites too?

And if there is a super admin to control all of the multisite websites then is there also still regular admins to each individual websites so you can go make specific changes to each individual website, like the contact page info, etc.?

Thanks for helping me!