Can you please explain how I can give someone the perms to do sth?
Or how does the system work?

As an admin, you can run the /trust <username> convenience command to move someone into the trusted group. You can also manage through the /permissions GUI. Permissions in Factorio are group based, so if you want per-person control, you need a lot of groups. Some in-progress work is being done to allow usage of an auto group assignment based on username.

As this is a scenario, not a normal mod, the system only works when hosted as the specific scenario, not any game - which means existing saves won't have access to this. It's possible to hand patch this in, but that's unsupported.