I recently graduated with a BSc in applied mathematics and considering on applying for a PhD. In fact, I contacted a supervisor and he seems some what interested in my undergraduate academic performance. He also sent some articles to read so that I get an idea of what sort of problem is there to be analysed in the PhD, and of possible methods to follow. I read them, however I do not understand everything in those papers as I am not familiar with some of the methods used. However, as I have a basic background knowledge from undergraduate coursework, I believe, I can study those methods in depth and gain knowledge. But it would obviously take couple of months for me to learn the material. Although my PhD wouldn't start (if I get selected) for another 6 months, I have to tell the potential supervisor about what I read in the articles he sent and how much I understand.
So, if I say like I didn't understand all the details, but I intend to learn them before the start of the PhD, does it look negative? Does supervisors expect us to know everything before the commencement of the research?