1.  Go to Accounts Payable, Configuration and Activity Types.
2.  Select New Activity Code.
3.  Enter in the appropriate Activity Code and Activity type.  Note: If you have different Accounts Payable offices in different provinces you may need to set up different Provincial Activity codes.  
4.  Enter in the the appropriate GST and PST Rebate Factors
5.  Mark the checkbox for 'Eligible for provincial rebate' if the province is eligible for a provincial rebate.
6.  Save and Close

To then use the Activity Types:
1. In Accounts Payable > Records > Invoices > open the desired invoice or create a new one
2. Enter the required information on the Invoice tab and then select the GL Distribution tab
3. Enter the desired debit and credit for the main distribution
4. Select the distribution drop down in the left corner
5. Select the GST Rebate and/or PST rebate areas and select the applicable PSB codes
6. Enter any other information on the record
7. Save and close