Once the roles are created, they can then be attached to specific users. This is done in the application itself at runtime. 

To do this, go to the user's record in the 'User' application tab and drilldown to 'Roles'. Then click '+' to add a new role, select the role and click Update. 

Alternatively you can select the role and click OK using the Quick Entry in the Roles tab below the user record. 

Note : Only an administrator user can see and change the Roles of a user. Other users will not be able to see the Roles drilldown.