Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
In Legacy Scoutbook - under Messages area - if a scout is listed under the Scout area on the far right they can receive messages.
If under the Scouts Profile, they have an email - they might be able to receive messages.
Parents and Scouts can use the attached PDF to set up a log in for the Scout. Then the Scout can log into Legacy Scoutbook (scoutbook.scouting.org) and that SHOULD enable them to get Messages through Scoutbook.
@MohamedArafa - there is no check list that i recall. There is just the help section. The real issue is that units use or DONT use scoutbook in any number of ways and to the extent that they desire to. There is no universal use of the system.