What to study if I want to learn more about time?

Hi, I have been very interested in the topic of time for a few years of my life thus far. I haven't been able to actually study it because, according to a physics and cosmology professor, it isn't really that well understood even up to today. Can anyone direct me a book or website that gives the details and equations behind time. I would like to strengthen my understanding of it and, perhaps, make it my feild of research during my undergradute and graduate years. Im hoping to possible make some contributions to it as well. Thank you!