You're missing a comma after tblSales.Principal. Once you've added the
comma, try this ...

First copy the SQL text that I posted, with your modifications to the field
and table names - and not forgetting that comma - to the clipboard. Now from
the Insert menu, choose Query. In the New Query dialog box, accept the
default, Design View, and click the OK button. If Access displays a Show
Table dialog box, click the Close button. Now from the View menu select SQL
View. In SQL View, all of the text should be highlighted. Leave it that way,
and from the Edit menu choose Paste. This will paste in the SQL text from
the clipboard, replacing the highlighted text. From the View menu, select
Datasheet View to see the result.

From the View menu again, select Design View. This graphical design grid is
how you will probably create most of your queries. You rarely have to create
queries in Access by typing SQL statements like the one I posted. But you
will often get answers to questions in this form, because it is easily
pasted into a newsgroup post, so it is much faster and easier to answer
questions about queries this way than to attempt to describe the
step-by-step process of creating the same query using design view.