Accrual is a method of accounting for expenditures (costs) or income for particular activities or events. In RiskyProject this accrual is at the activity level and can occur at the beginning of an activity, the end or be prorated based on the % of the activity complete. The accrual method that you select depends upon how your accounting system works. Depending upon your project and how the duration of activities, the method can impact cash flows. A good default setting is prorated as this will account for work completed if activities span reporting periods or periodicity set in the Cash Flow view.
You set the default accrual methods for cost and income in the Project Options > Cost tab.