Thank you for your post.
When you specify a calculation, the dialog box has an upper an lower portion. In the lower portion, there is a large box that allows you to enter the calculation.
The functions are in the upper right, and the fields are in the upper left.
If the calculation you want to enter is:
Rightwords ( first name field; 1 )
The "Rightwords" is the function, and it contains two components. The text field or text string, and the number of words you want to extract. In this case, it appears you want to take the right most word in the first name field.
In the fields listing (upper left), find the first name field and double-click on it. The field will now appear in the calculation area. Depending on relationships, it may also be preceded by the table name. If your first name field is named "FIRST NAME", then the calculation should show:
Rightwords ( FIRST NAME; 1 )
Let me know if you need any further clarification.