query that spans servers/DB

Hello experts,

i am having trouble writing a query where i need to grab information from tables that are in different databases on different servers. How would i go about accomplishing that?

i get the following error .

Msg 7202, Level 11, State 2, Line 21

Could not find server 'SAP-PROD' in sys.servers. Verify that the correct server name was specified. If necessary, execute the stored procedure sp_addlinkedserver to add the server to sys.servers.

i have tried

[server name]. database name. dbo.tablename.

and it still gives me the error message.

Thank you in advance