A crossword puzzle is a puzzle in which words are guessed from clues or definitions.  These words are placed into a grid of black and white squares with the letters in either horizontal or verticle orientation.  The letters are arranged from left to right, top to bottom, with the black squares separating the words or phrases.

The earliest known publicised crossword was published in the New York World by Arthur Wynne in 1913.  Other notable dates are 1924 when the first crossword book was published by Simon and Schuster.

In the present you can find crossword puzzles in print (such as a newspaper or magazine), on your computer (like a computer game) or even online.  You can even go online to get free printable crossword puzzles.  

If you feel like trying to make a crossword puzzle like the professional puzzle makers do it, you could try to do it on paper.  An easier solution is to use a free online crossoword maker that will make the puzzle for you - all you have to do is supply the words and clues.