How can I relate my undergrad works to professors research areas? Recently, a professor answered my email for a graduate position. He asked me to tell him to what extent I am aware of his research. I have a background research experience in his research area, I can understand his papers generally but I can't talk about them in detail. Since he asked me to answer this question in detail, please help me to how can I talk about his research area?

Moreover, he asked me to tell him about a specific direction that interests me for my future studies and the way I can make a contribution to his research. 
Answering this question is hard for me because I don't know how to define a specific direction that doesn't make me limited and lose the opportunity of working with him.

Please help me if you have any ideas.
Thanks in advance.
Answering this question is hard for me because I don't know how to define a specific direction that doesn't make me limited and lose the opportunity of working with him.


This is a thoughtful response on his part. He is not asking for you to send him a dissertation proposal, but maybe something four or five times as broad. Maybe something like "I'm interested in interventions to support learning in recent immigrants to [your country]," rather than "The effect of X intervention on mathematical learning on late teenage refugees to [your country] who did not receive formal education in their home country."

It's not a quiz to see if you come up with a good enough one and "lose" the opportunity to work with him (unless he's a nasty person). More of a determination whether you two are a good scientific fit.