The following Microsoft SQL Server T-SQL code sample with order and order detail tables demonstrates the usage of SHOWPLAN:

USE Northwind
GO

SET SHOWPLAN_TEXT ON

-- SET SHOWPLAN_ALL  ON

-- SET SHOWPLAN_XML  ON

GO

SELECT *,

       o.OrderID    AS OrderID,

       o.CustomerID AS CustID

FROM   Orders o

       INNER JOIN [Order Details] od

         ON o.OrderID = od.OrderID

       INNER JOIN Products p

         ON od.ProductID = p.ProductID

GO

SET SHOWPLAN_TEXT OFF

GO

/*

StmtText

  |--Hash Match(Inner Join, HASH:([o].[OrderID])=([od].[OrderID]))

       |--Clustered Index Scan(OBJECT:([Northwind].[dbo].[Orders].[PK_Orders] AS [o]))

       |--Hash Match(Inner Join, HASH:([p].[ProductID])=([od].[ProductID]))

            |--Clustered Index Scan(OBJECT:([Northwind].[dbo].[Products].[PK_Products] AS [p]))

            |--Clustered Index Scan(OBJECT:([Northwind].[dbo].[Order Details].[PK_Order_Details] AS [od]))

*/          

Related article:

Displaying Execution Plans by Using the Showplan SET Options (Transact-SQL)

http://www.sqlusa.com/bestpractices2005/executioninms/