COM DCOM AND SYSTEM AND WORK FLOW

HOW CAN I USE API FUNCTION IN VISUAL BASIC
AND WHAT THE BASIC CONCEPT BEHIND COM AND DCOM ARCHITECTURE AND WHAT IS THE UTILITY OF COM DCOM ARCHITECTURE WHERE IT CAN BE USED .
TELL ME THE SITE FROM WHERE I CAN DOWN LOAD THE METERIAL RELATED TO COM DCOM ARCHITECTURE AND API FUNCTION USAABLITY.

WHAT IS WORK FLOW APPLICATION IN GENERAL AND WHAT TYPES OF WORK FLOW APPLICATIONS ARE THERE .