Complex sentence: JMUN 2015 has a staff of 55 undergraduates from Jahangirnagar University, these staff members are organized into three groups: the Secretariat, the Senior Staff, and the Junior Staff.
Split into simpler sentences: JMUN 2015 has a staff of 55 undergraduates of Jahangirnagar University. These staff members are organized into three groups: the Secretariat, the Senior Staff, and the Junior Staff.