Please explain the string theory?

String theory suggests that fundamental particles in the standard model of physics (quarks, muons, neutrinos, etc.) arise from very very very tiny strands of energy. Their shape and frequency of vibration determines what type of particle arises.

Already I can't explain it because you call yourself "common folk," which essentially means you know very little of the subject, and string theory is highly complex and requires an elementary understanding of particle physics, but nevertheless, I'll do my best.

String theory is an attempt at a grand unification theory (GUT), which unifies all of physics under one fundamental concept. This concept is that all subatomic particles are made up of vibrating strings that produce different particles because of different vibrations, much like different guitar strings produce different notes. These strings also have a slew of other weird properties that cause other natural phenomena.

Honestly that's about all I can tell you without going into technical detail, and if you can't understand that, I can give you no hope of ever understanding it because you've probably never read a book about particle physics in your life, which is sad considering you are made of them. Give them some decency and acknowledge their existence by learning about them. Surely it couldn't hurt you.