Solar flares are the most energetic events in the solar system and are associated with the release of high-energy radiation, ejection of hot gas and particles towards the Earth, causing severe disturbances to our space environment. Understanding the physical mechanisms responsible for flares still remains one of the most outstanding questions in solar physics. In this talk I will discuss what solar flares are and how to study them by combining observations from space-based satellites with predictions from numerical hydrodynamic models.