How do all these people get paid?

When I hire freelancers, I use a Work for Hire contract, meaning that I own the copyright to the product after I've paid for it. I would not offer royalties or commissions. As for how all those people get paid, it's in their contract how they get paid.

This is a bit of a broad question because of the difference in those professions.

when we IMers pay people to work on our things, we pay them up front or after the work is done and that's the end of it.

I don't give people a cut in my business because they helped one time.

In regards to traditional publishers, authors get paid royalties. Usually when a book is accepted an author will get an advance, a chunk of money based on how much the publishing company thinks the book will sell. Once the book sells enough copies to pay off the advance (which can vary widely), the author will start earning royalties - a percentage of sales of his/her book. The percentage can be pretty small, and even less if they have a literary agent, who will take a percentage of the author's cut. They'll get royalty checks in the mail monthly or quarterly, depending on the contract.

As for editors and cover designers, if they work for a publishing house, they probably get paid a regular salary. In other words, they get paid the same regardless if a book they worked on is a bestseller or a flop. Freelance editors and designers will more than likely be paid by the job. Some might negotiate a split-commission type deal with the author, but I think that's pretty rare.

More than likely you're looking at a one-time fee for freelance editors, graphic designers, etc.

They probably hand over the copyrights to the company they work for.

When it comes to movies and extras and actors, etc, I can tell you that the extras get an hourly rate for the time they work and that's all. The big name draw cards get a mammoth fee for appearing in the movie and I believe they also get some sort of royalties but from what I remember, it also depends on the actual contract.
I know because I spent a number of years doing that kind of work (not being a big name though.)

With my writing work, it's a one time deal I do the work and my client owns that work. I don't make a commission. Some writers are different, especially copywriters where they can draw big money for their clients.

Most authors get royalties in addition to fees.

I hope that helps a bit. Some scenarios differ of course so you need to consider whatever you do and work out how you want to be paid.

I always prefer one time payment, so after that whatever money make, it's all mine.

It depends entirely on the contract you have with that individual. I NEVER agree to royalties when hiring a ghostwriter. I always pay a flat fee and have the freelancer sign a "ghostwriting contract." It's good to make sure that all parties involved have a good understanding of the employment contract before work commences.