Subjected to be changed by Google.
It is strongly advised that you make a backup file before sharing.

On desktop

1. Open your file in Google Docs. You'll notice on the upper right corner, next to your logo, there's a "Share" button. Click it.

   

2. You'll get a box. Under "General access", click the arrow head beside "Restricted".

   

3. Change it to "Anyone with the link".

   

4. Then click the arrow head on the right beside "Viewer". In the drop box that appears, you'll be able to select what others can do to your file ("Commenter" can only comment, "Editor" can directly edit your text). After that, click the "Copy link" button and send it to your editors.

   

That's it.

On mobile

1. Open your file in Google Docs app. On the top right corner there's a symbol of a person with a plus sign. Click it.

   

2. Then click the lock symbol at the bottom with the word "Not shared" beside it.

   

3. The next window is pretty much the same as on desktop. Just follow the same steps 2 to 4. The "Copy link" button is the chain link symbol next to "General access".

   

I've been doing that a lot so I'm good.

This is very concise, and exactly what I was hoping to see. Thank you very much.

Problem: I don’t feel comfortable sharing emails with someone. Also, I typically use Word rather than Google Docs. What do you do if Google Docs or conventional sharing methods are not available/desirable?

Note: I currently just have the chapters PMed to me and I copy and paste to my notes app then PM it back. I’m currently the sole editor, but what’s a more anonymous way to collaboratively edit?

7834841
One of my own friends has an email address made specifically for sharing her works with others for editing. If you don't want to use your main email, you could always do that--make an alternate email under a fake name.