In each compartment, you will have eight seats in a section of a compartment. Generally, any number which is getting divisible with 8 with zero reminders will be side upper berth. When you get into a compartment and start travelling from the first section to the last section, you will have 9 sections and each section will have 8 seats. Seat No: 8,16,24,32,40,48,56,64,72 and 80 will be side upper. in your case, it is the side upper berth in the 3 rd section of the B2 compartment.
B2 32 SU means in B2 compartment your seat number is 32 which is happened to be a side upper berth. B2 is the coach, SU is side upper 32 is the seat number.