Complex sentence: The Penny Black, the world's first adhesive postage stamp of a public postal system, was issued by the United Kingdom of Great Britain and Ireland on 1 May, 1840, for use from 6 May of that year.
Split into simpler sentences: The Penny Black was the world's first adhesive postage stamp of a public postal system. It was issued by the United Kingdom of Great Britain and Ireland on 1 May, 1840, for use from 6 May of that year.