William Gallagher, Apple Insider:

Once you understand how it works —and know the right sequence of steps to go through —then file sharing with iCloud Drive is tremendous when it’s working. It’s just that setting it up is surprisingly confusing, so let’s walk through it.

And:

The way that you share files from iCloud Drive varies slightly between iOS and Mac, but the principle is exactly the same on both. You find your file, choose Share and then specify who you’re sharing it with.

Remember that your file has to be in iCloud Drive and remember that you cannot do this with a folder. You can’t even select two or more files and share those. It’s one file at a time, as tedious as that is.

I really want to use iCloud Drive. But I end up using Dropbox. It’s just easier.

That said, this is a good “how to”, well written, absolutely worth reading, just to know how this works.