How to approach this requirement

Business overview:

For every organisation account management will be the core functionality. The account management should include the foll:

customer - company - vendor.

1. customer info

2. vendor info

3.organisation info

4.material info

5.purchase order info

6.sales order info

7.subsequent documents such as delivery doc,invoice doc n accounting doc info.

Reports:

1.purchase order line item wise report.

2.open purchase order.

3.sales order line item wise report.

4.open sales order report.

5.open invoice item wise.

Im new to ABAP, Please someone guide me how to approach this requirement. Which are the tables and fields i need to work with?

Thank You.

Ashwini