The COSINE experiment is a joint effort between the KIMS-NaI and DM-Ice experiments to test the DAMA’s claim on the WIMP discovery. It consists of 106 kg of NaI(Tl) crystals immersed in a 2 tons of liquid scintillator as an active veto. The construction of the first phase of the experiment, called COSINE-100, was completed in the summer of 2016. The physics run of the experiment has begun in September 2016 at the Yangyang Underground Laboratory in Korea. The current energy threshold is set at 2 keV with 90% signal efficiency and the background level is 3 dru (Differential Rate Unit- count/keV/kg/day) at 2 keV. A background study and the performances of the COSINE-100 detector are presented.