Lets build SQL query which will return the resultset where tables orders and customers joined by orderno field:
Place tables on the Work area and check desired fields.
Drag custno field from orders table onto custno field in customers table.
Right-click on the Link...
...and modify Link conditions as desired.
Press OK button, and your SQL query will be built.
Your SQL query is ready to run.
Press F9, and SQL query will be executed.