You can't use the Web Connector with QuickBooks Online Edition. The Web Connector is for use only with desktop versions of QuickBooks.
QuickBooks Online Edition provides an HTTP API that you can use to communicate with it. Basically, you send HTTP POST requests with XML data to the QuickBooks Online server, and it responds with XML responses.
There is some documentation showing the setup process in the QuickBooks SDK and on my wiki:
QuickBooks Online setup process
And some example XML requests/responses as well:
Example qbXML request/response
Further documentation on qbXML requests you can send can be found here:
QuickBooks OSR
It should be noted that you cannot create paychecks. Intuit does not give you the ability to create paychecks programatically. The closest you can get is creating Time Tracking sheets with the TimeTrackingAdd request, which can then be converted to paychecks/payroll entries within the QuickBooks Online GUI.