There are actually 7 tables.  StaffT is joined to OrderT also.  And StaffID is in the main form.

The append query is what you are looking for.  Check out the Append Query video.

You will not append data into autonumber fields.  They will take care of themselves.

In your button, you will need something like this to run the query:

Private Sub NewFlexiPeriodBtn_Click()
    DoCmd.OpenQuery "appendFlexiQ", acViewNormal, acEdit
End Sub

Thank you Matt, so do I just omit the two autonumbers when I make the query? I will try this tomorrow when I'm in work.

Yes.  Just populate the fields you want from your "template" table.

Hi Matt, no this is not working.  I am getting an error saying type conversion failure, key violations, lock violations and validation rule violation".  

Currently, I click the 'new (blank) record'.  At the top of the main form I have a dropdown box to choose a date (from OrderDateT).  These are the valid days which start each Flexi Period.  Another dropdown box to choose the member of staff (from StaffT).  The subform has two dropdown boxes (Product) and (Location)  the product is 1 of 20 days i.e. 1Mon, 1Tue up to 4 Fri (this covers the 20 days of attendance over 4 weeks, and also a Location, Home, Office etc.   I have populated the append table with the primary keys for the dropdown boxes. There is also a date field which is calculated from the product (adding relevant days from OrderDateT.
The primary keys are not allowing me to populate the OrderDetailsT.

I can add the rows manually, but I want the member of staff to be able to click a button and all 20 rows are added.  Help!!

Solved!  thanks for your help Matt.

Your error message should also give the number of records affected by each type of violation.  What type and how many of each error are you getting?   What table.field's are you trying to append to OrderDetailsT?  

For testing, I would work directly with the underlying table that you want appended (OrderDetailsT) and the append query you are building and deal with the forms after the query is functional.  

If you can post an image of the query and the table, that might help.

I took too long typing...Glad I could help.