To create a field in a query you just type in a name for the field on the Field (top) line in your query. In this example we used
MySortField:
with the colon at the end, and then add whatever expression you want to get the results you need.
In this case, I wanted to find the first 3 characters in your code field so we used
Left([YourCodeFieldName],3)
Put them together on the Field line of your query like this.
MySortField:Left([YourCodeFieldName],3)
When you run the query you will have a column called
MySortfield
at the top, and the 3 character values you want in the column. You need to replace [YourCodeFieldName] with the actual name of your field.
If you create these fields in the query, then when you create the Report with the wizard, you can just add the fields from your query rather than trying to create them in your Report.
Start slow. Create the query with whatever Table/Query you want, then try creating one new field. See how it goes and post back with any questions. If you have problems, post what you have tried so we can see it and advise from there.
Good luck.
Paul