1. Here is a good summary of class selection from UC Berkeley/Haas
https://www.haas.berkeley.edu/MBA/academ ... index.html
2. This explanation from Northwestern/Kellogg might be helpful:
https://www.kellogg.northwestern.edu/scr ... d_summ.htm
3. It should be noted that many MBA programs do not require students to select a concentration or major.
A concentration or major typically requires that students complete a small number of mandatory courses and then requires students to choose a set number of courses from a list of courses. Even if one decides to change to a different concentration during her MBA, the courses that she has already taken could still be counted as general electives against the degree requirement.
This concentration at Columbia is a useful example
https://www0.gsb.columbia.edu/finance/st ... centration
Here is the list of majors at Wharton
https://www.wharton.upenn.edu/mba/academ ... majors.cfm
4. It is not typical to declare a concentration per se when you apply. However, it is valuable to have a clear idea of what you want to study when you make your case for admission.