You can read about this painting at this web site, with info about Pablo Picasso and his works. Here's a bit from the introduction:
Guernica shows the tragedies of war and the suffering it inflicts upon individuals, particularly innocent civilians. This work has gained a monumental status, becoming a perpetual reminder of the tragedies of war, an anti-war symbol, and an embodiment of peace. On completion Guernica was displayed around the world in a brief tour, becoming famous and widely acclaimed. This tour helped bring the Spanish Civil War to the world's attention.
This work is seen as an amalgamation of pastoral and epic styles. The discarding of color intensifies the drama, producing a reportage quality as in a photographic record. Guernica is blue, black and white, 3.5 meters (11 ft) tall and 7.8 meters (25.6 ft) wide, a mural-size canvas painted in oil. This painting can be seen in the Museo Reina Sofia in Madrid.
Interpretations of Guernica vary widely and contradict one another. This extends, for example, to the mural's two dominant elements: the bull and the horse. Art historian Patricia Failing said, "The bull and the horse are important characters in Spanish culture. Picasso himself certainly used these characters to play many different roles over time. This has made the task of interpreting the specific meaning of the bull and the horse very tough. Their relationship is a kind of ballet that was conceived in a variety of ways throughout Picasso's career."