The present invention relates to a wireless communication system and, specifically, to a method and an apparatus therefor, the method comprising: a step of configuring a plurality of carriers to which an SL communication is applied, wherein an SL resource pool is periodically configured in each carrier; a step of selecting one of the plurality of carriers as a serving carrier; a step of selecting a transmission resource among the SL resource pool in the selected carrier; and a step of transmitting the SL signal using the transmission resource, wherein a frequency of a process of reselecting the serving carrier is less than a frequency of a process of reselecting the transmission resource among the SL resource pool in the preselected carrier.