Either go to files tab -> add cloud storage then select sharepoint! You can here add a library url or browse a site! ( you need access on this library ) Or you click the + at the tabs bar and choose library and do the same procedure as above! For people to access the files they need permissions on that library as well!
Thank you for your answer, I tried it, but I can not find the option "add storage", I think I do not have rights in my company (I checked a little on the net). Can you confirm ?
However, I found the option "add cloud storage" by another path (photo) and when I want to use this option (first element of the photo), he asks me the URL of a library and I do not know if it works, but I tried some tests and I failed each time .... Either I do not have rights or I do not know how to find the right URL
This didn't work as I only have access to a subfolder of a channel on the sharepoint, not the channel itself.
I found a workaround however by adding the sharepoint as a website tab. Works like a charm. From access management point of view it is not as easy, as you have to make sure all members of your team also have the appropriate permissions to the sharepoint.