1. Type the Simulink model and add the signal building module to the model. In the edit window of the signal generator module, select New Signal to create a new signal.

2. Select "signal type" as "square wave" in the editing window of new signal, and set parameters such as amplitude, frequency and duty ratio of square wave.

3. Click OK to save the signal settings and close the editing window.

Right-click the signal generator module and select Output to connect to the module that needs to use the square wave signal.