Sever roles are found in the Server Manager application. Once you install a Windows Server OS, you have multiple choices as to what you want your server to be used for. Microsoft acknowledged that and made it to where you do a base install and then pick and choose what you want your server to do on top of the base.
If you support a primarily Window’s environment, it is important to know all the server roles and what they can do. The references link below is a good place to start, enjoy!
Click the Server Manager icon on the bottom left of the Windows Taskbar and Navigate through “Roles and Features” which will look different depending on your version of Windows Server but they do the same things.
Depending on what you are installing will depend on what steps to take next, just make sure to read each section carefully. For example, on installing the “DHCP” service, you have the option of configuring lease times and address pools, these can be done later => but you should not rush through the installation of any role or feature.