Once you connect your cloud storage to Documents, you can easily share a link to uploaded files and folders with other people. This is extremely useful when you need to quickly share some files so that other people can view, download, or collaborate on them.
Due to the workflow peculiarities of different clouds and depending on what cloud you use, there are two scenarios of how to create a shareable link.
Google Drive, Dropbox, Box
These clouds allow you to generate a link right in the Documents app. To share a link, open your cloud folder in Documents > find the file or folder you'd like to share > tap ... on it > tap 
Share link. Once a link is opened by the recipient, they can view and download the shared file or folder. If you would like to change the access setting so that people can, for example, edit or comment on your files, you can do it either in a browser or in a dedicated app. Here are the detailed instructions for each cloud:
iCloud, OneDrive, and other storages
Due to the performance specifics of these clouds, you need to access either the website of your cloud or a dedicated app to be able to create a link. Here are the detailed instructions on how to create a link for some of the clouds:
If you don't see the needed cloud in the list above, please look for a relevant article on the website of your cloud storage.