These roles are the default server level roles at the instance level. You can find the brief description about these roles below.
|sysadmin||sysadmins is the most authoritative user at Instance level. They can do everything.|
|serveradmin||serveradmins can change configuration at Instance level and turn off instance.|
|securityadmin||Security admins can manage the logins and reset their passwords, run “grant, deny, and revoke” commands at the instance level. They can also run “grant, deny, and revoke” commands on databases they have access to.|
|processadmin||processadmins can shut down a process on the instance.|
|setupadmin||setupadmins can create and drop linked server using TSQL.|
|bulkadmin||bulkadmins can run “BULK INSERT” command.|
|dbcreator||dbcreators can create or restore databases, and modify and drop existing database.|
|public||Even if no privileges are granted to each login created, it is the default privilege granted initially.|
Apart from these roles, you can create server level roles. You can use the following article.
“How To Create a Server Level Role in SQL Server”