Microsoft SQL Server Not Showing Server Name in object Explorer
It looks like you have only installed SQL Server Management Studio (SSMS), and not SQL Server.

SSMS is the tool used to connect to and manage SQL Server Instances, if you haven't installed a SQL Server instance you have nothing to run your queries against!

Press Windows Key + R (Run) and type services.msc, check to see if the 'SQL Server' appears and that it is running.