Dear Renatas,
Please refer to online help for "Cash flow for the class":
http://help.sap.com/erp2005_ehp_02/helpdata/en/26/c867c6964311d1a5220000e839d005/frameset.htm
In master data maintenance for the classes, you can display a fictitious cash flow showing all the flows that would be generated for a fictitious purchase with a nominal value of 100,000 or 100,000 units, based on the conditions entered.
This is used for simulation of the cash flows with the coditions. The nominal value or units are hard-coded here.
To create a real security transaction, you may use tcode TS01 or FTR_CREATE, there you may enter the actual nominal value or units for your contract.
Best regards,
Jasmine