The idiom "sum and substance" refer to -

• Sum and substance
English Meaning: the general or basic meaning of something.
Bangla Meaning: সারকথা, মূলকথা.

Ex. Sentence: Mark the book to skim through the sum and substances before the exam.
Bangla Meaning: বই দাগিয়ে রাখো যেন পরীক্ষার আগে মূল অংশগুলোতে চোখ বুলিয়ে যেতে পারো।

Source: Website Lecture.