If you were using a windows account, you would specify a login credential, there are options to either use credentials from the login accessing the account, or you can specify to have the linked server service all requests via a different credential.

See below:

Your code for the linked server to use windows credentials from the requesting user:

EXEC master.dbo.sp_addlinkedsrvlogin @rmtsrvname = N'TEST', @locallogin = NULL , @useself = N'True'

GO

If you wanted to service the linked server login with a different windows login:

EXEC master.dbo.sp_addlinkedsrvlogin @rmtsrvname = N'TEST2', @locallogin = N'Domain\Username', @useself = N'True'

GO

Glad you're on the right track.