Process Flow of Master Data Entry 
A) Creating business partner data

You cannot create the issuer from the class master data.
B) Creating class master data and securities account master data
C) Position indicators
The position indicator determines the position management and valuation parameters for a class at company code and securities account level.
You can maintain position indicators if you have created class data and securities accounts.
See also:
Position IndicatorD) Maintaining security prices, reference interest rates, index values, and exchange rates
You find the functions for manually entering
Security Prices, Reference Interest Rates, Index Values and Exchange Rates in the securities area under Environment ® Market data ® Manual entry of market data.