Hello and welcome to the community!
That’s great to hear that you have chosen Xibo and yes adding media is quite straight forward and can be easily achieved by a basic user.
We have User documentation which would be of use to you as you explore the system as well as Administration documentation with regards to set up etc.
We also have some great guides: How to create a simple Layout
You can control access and interaction for users using Features and Sharing options in our latest v3.
The Playlist Dashboard and User might also be a good option for you here, which would take minimal set up from you and instruction to the users who would use it: Utilising the Playlists Dashboard
We do have some online training courses here which are short video tutorials which cover the basics: Xibo Signage Training Homepage
I would however like to point out that running a Xibo Player on RPI is not an option I am afraid, see the Q&A here for more information: Can I run a Xibo Player on my Raspberry Pi (all variants) | Xibo Open Source Digital Signage
Hope all goes well 