1. Set up all the local users you need in the 'Users' page in the VPOP3 settings. The usernames & passwords do not have to have any relation to the ISP's accounts. These are the details which the users will put in their email clients (eg Outlook) to collect their mail from VPOP3.
2. Go to the Mail Connectors page
   
3. Check that there is a Connection method defined under the 'Connections' entry at the left. This tells VPOP3 how to connect to the Internet. If there isn't one, click on 'Add New' under the Connections entry to create one. (If you have run through the initial setup wizard, that will have created one for you).
4. Under the 'Mail Collector' item on the left of the screen, click 'Add New'
   1. On the first page, put a name in the Mail Collector Name box. This is purely for your reference, so can be anything, but it is best to make it relevant to the ISP account since it is used in error & status reports. Choose 'POP3 Download' since that's what you want. Press Next
      
   2. Enter the ISP POP3 server name, account name, password as provided by your ISP. Choose the 'Send all incoming messages to a specified user or list' option. Press Next
      
   3. Choose the VPOP3 user account who you want the messages from this ISP account to go to. Set the other options as you wish (the defaults are sensible). Press Next
      
   4. Press Finish
5. Repeat Step 4a-4d for all the ISP POP3 accounts
6. Still in the Mail Connectors page, click on Connector Schedule, and ensure there is a connection schedule defined for VPOP3 to collect mail from the ISP accounts. (If you have run through the initial setup wizard, that will have created an initial schedule for you).

All the settings you make you can change later if you wish,