William Caxton did not invent the printing press: in fact, that honour belongs to a German inventor called Johannes Gutenberg. He developed the world's first printing press in 1440. (See the first reference link for more information.)
In contrast, the merchant and diplomat William Caxton was the first person to introduce printing into England. He established a printing press (the first of its kind in England) at Westminster in London in 1476 - some three decades after Gutenberg invented the press.
Thanks to his press, Caxton became England's first bookseller and sold some of the era's most popular and important books, like Geoffrey Chaucer's The Canterbury Tales. He also personally translated many famous works, including Thomas Mallory's Le Morte d'Arthur. (See the second reference link for more information.)