What is the function of a conjunction How do you use it in a sentence?

Conjunctions join Words, phrases, and clauses. Perhaps the most common conjunction is the Word and.

Tommy's brother went to the store, and bought food for the picnic.

Other conjunctions are but and or. Adverbs can also be used as conjunctions (conjunctive adverb).

I like science fictions movies; however, my wife prefers comedies.