FLASH, the Free-electron LASer in Hamburg, is a worldwide unique source for extremely bright ultra-short laser-like pulses tunable in a wide spectral range in the extreme ultraviolet and soft x-ray region (Ackermann et al 2007 Nat. Photonics 1 336-42). To fully exploit the features of this new generation of light sources, a user facility with efficient radiation transport to the experimental area and novel online photon diagnostics capable of characterizing the unique parameters of the FLASH radiation has been built. It serves a broad user community active in many scientific fields ranging from atomic and molecular physics to plasma and solid state physics as well as chemistry and biology. A special focus is placed on the exploitation of the ultra-short FLASH pulses using pump-probe techniques. Thus, the facility is equipped with optical and THz sources synchronized to FLASH. This paper gives a detailed overview of the FLASH user facility.