Every user has a role, and a role can have a profile assigned to it.
If a profile has certain permission, then users who belong to the profile have that permission. For example, if a profile is permitted to edit or delete records, then the users of the profile can edit or delete records. On the other hand, you can also assign privileges directly to a role.
To learn more about Users, click here.
To learn more about Roles, click here.
To learn more about Profiles, click here.