In an inducible operon, the inducer is often the in the pathway being regulated; the inducer binds to the thus rendering it

substrate; repressor; inactive

In the absence of the inducible operon, the repressor operon will be bind to the gene and prevent its transcription. When the substrate present, which is inducible operon,  it will bind to the repressor so the gene can be transcripted. This mechanism can be seen in lac operon of the lactose.