You can make donations with and without user accounts. These records are created and stored as charges.
{  
  "charge_status":"charged",
  "amount":"2500",
  "net_amount":"2397",
  "fees":"103",
  "currency":"USD",
  "giving_type":"General Fund",
  "charge_date":"1497638090",
  "deposit_date":"1497838090",
  "recurring_transaction":false,
  "fees_covered":false,
  "organization":{  
     "widget_id":"*****",
     "account_id":"user_*******",
     "created_date":"1487795327",
     "name":"Test Organization",
     "phone_number":"5551231234",
     "website":"https:\/\/tithe.ly",
     "address":{  
        "street_address":"123 Test Ave",
        "city":"Lawrenceville",
        "state":"GA",
        "postal":"30043",
        "country":"US"
     },
     "giving_types":[  
        "General Fund",
        "Offering"
     ],
     "bank":{  
        "account_number_last4":"6789",
        "name":"TEST BANK",
        "country":"US",
        "currency":"USD"
     },
     "legal":{  
        "entity_type":"organization",
        "organization_name":"Test Organization INC",
        "first_name":"Mike",
        "last_name":"Rogers",
        "date_of_birth":"5\/23\/1985"
     },
     "organization_id":"org_*******"
  },
  "donor_account":{  
     "created_date":"1486410076",
     "email":"janedoe@tithe.ly",
     "first_name":"Jane",
     "last_name":"Doe",
     "address":{  
        "street_address":"123 Test Dr",
        "city":"Lawrenceville",
        "state":"GA",
        "postal":"30043",
        "country":"US"
     },
     "phone_number":"5555551234",
     "account_id":"user_*******"
  }
}