Proposed is a method for performing wireless communication by a first device. The method can comprise steps in which the first device receives from a second device a first physical sidelink control channel (PSCCH) or a first physical sidelink shared channel (PSSCH) comprising information relating to a second synchronization source, determines synchronization of the second device on the basis of the information relating to the second synchronization source, and performs the synchronization of the second device on the basis of a reference signal of the first PSCCH or first PSSCH. For example, the second synchronization source can comprise a synchronization source having a highest priority configured beforehand with respect to the second device.