The rain below temp means a dry month. The opposite is a wet month. But not only this, depending on the whole graph patterns you can know your climate characteristics. If the temp plot is always above rain, you're on a dry, arid climate. Temp always below rain is a tropical climate. There's a relation between the climogram and Köppen climate classification.
I would like to thank Meteo Aerolugo Weather station in Spain for creating and helping me with these graphs.