You wish to know how to manage administrative registrations and donations. These are transactions that you complete for your constituents, when they call or fax in information.
You can complete administrative registrations from Account -> Website Admin Mode (upper right hand corner of the dashboard).
Using the Website Admin Mode allows you to register constituents with fewer required fields and all payment methods enabled. Website Admin Mode will only be enabled for your session and will not effect users on your site.
This method can also be used for donations or product sales. However, if you are administering a Pledge website with personal fundraising pages, please use this method of administrative/offline donations, so that your participants can receive credit for their donations.