Hi Sree -
You've probably figured this out already, but YOU need to know the name of the computer on which you installed Tableau Server - we can't tell you that in Desktop. Just type the computer name into that box, and you should be ready to roll.
Had the same question , this is how got there
1/ Launch Tableau Server Monitor
2/ Go to Status on line Process see you will see computer name
Per Tableau :
On the computer or device from which you want to access Tableau Server, type the following URL into the browser: