Requirements gathering as a business analyst
The main approach for gathering business requirements is getting more ands more interaction with the end users / clients / business users. All these terms are more or less has same meaning in the industry technical jargon. But the usage of these words differs from company to company. As a business analyst first you need to have a formal /informal meeting with the business users to understand the functionality of the object in question. Understand the functionality from end user point of view and make clear notes of each and every step. Try to know the existing process (manual / automated) for the functionality and is there any difference between the existing and new functionality? Even if there is a little change in the existing functionality, you need to have a clear picture for that.
Once you understand the functionality and the requirement now make a clear document with the same understanding and write on a separate sheet about the point where you are not very clear. So, now since you have few questions with you, try to arrange a meeting with the end user once again to clear those points and in some cases you need to interact with the person who is actually working with this functionality at clients place, and sit with him understand what they are doing and clear your questions.
Though there are multiple ways of gathering requirements which vary from client to client, the above mentioned is the one which is a common and general way fo gathering requirements.