What are the theoritical background of common problems of freshmen?
Your question is a bit vague, but since you have posted it under "Social Sciences," I will discuss some social sciences concepts that might apply to some typical freshman problems.
First, what are some problems freshmen might experience? A freshman might be have a hard time adjusting to being away from home, might have a hard time adjusting to the academic world, or might have a hard time adjusting to the diversity of people encountered in a large university.
In the first instance, we might say that separation is part of the maturation process, with a freshman being away from his or her family for the first time. In the second instance, the freshman is encountering a new culture, the culture of academia. This could be viewed through the lens of anthropology. The new culture has a different language, different rules, different rituals, and perhaps different modes of dress. It might even have different food. (Dorm food is certainly not like the food one gets at home!) The freshman needs to acclimate to this new culture. In the third instance, sociological concepts about class and diversity might be relevant to adjustment. No matter what the earlier experience of the freshman is, he or she is likely to encounter people from different social classes and different backgrounds. This can create adjustment difficulties for some students.
The question is a bit vague, as I said, but I hope this is helpful.
For a good sociological angle, we can say that freshmen are in a transitional place in their lives. To use a fancy word that scholar use, we can say that they are in a liminal place in their lives. They are not in middle school and they are not quite accepted into high school culture. For this reason, there will be some discomfort. The freshmen feels it themselves, but also those of other grades. Mary Douglas speaks of being in-between and how most societies find this uncomfortable or even a cause for pollution. In the light of this, there will be anxiety and awkwardness until freshmen negotiate their own identity and space.