Question

pad parichay mai samucchaybodhak avyay kab lagta hai ​

Answer 1

hey!

pad parichay mein samucchyabodhak avyay tab aata hai jab koi shabd kinhi 2 vakyon ko jod raha ho(i.e. conjunctions)

Answer 2

sammuchaybodhak shabd is basically a conjunction. it is used to join two different sentences.

In your example, परन्तु joins  the sentences विद्यालय गए and वहा अवकाश था.

Hope it's clear now; good luck for your board exam :3