Authorizations are managed by means of security groups. A security group holds the settings that define what the members of the group are allowed to do.
When you make users members of a group, they inherit its security settings. Users can be members of multiple groups. Their authorizations will be determined by the total of all security settings across the security groups of which they are members.
Use the page "Security" in the system administration app to see the list of security groups. You can see the members of each group by clicking on the three dots on the right, then selecting "Show members." Use the button "Add" to add a person as a member to the selected group.