The present invention relates to a wireless communication system and particularly to a method and a device therefor, the method comprising the steps of: detecting an SSB, the SSB comprising 15 kHz-granularity-based offset information; determining, on the basis of the 15 kHz-granularity-based offset information, a subcarrier offset used to identify the frequency position of a CORESET linked to the SSB; and monitoring, on the basis of the subcarrier offset, the CORESET linked to the SSB.