I am not going to describe each role, as Microsoft has documentation explaining each role and its functions here.
Each System Role has its own function. You can install multiple roles on one server or on separate servers.Each Role extend the functionality of the SCCM.
Let’s install a new Role for SCCM. To do so, Open the Configuration Manager console, Select Administration, Under Site Configuration select Sites. Click on Add Site System Roles.
Leave all Default settings here and Click Next
Specify Different Proxy Server if required, Otherwise Leave Default and Click Next
Select the Role you would like to add to Existing Site Server and Click Next
Click Next To start adding the Role
Wizard will provide you an update with whether or not the role is successfully installed for not. Click Close to Finish.
That’s it. We have the new role added to existing SCCM Server.