Turret Raycasting Rotation Help

I'm trying to create a turret (like in a tower defense game) that targets enemies and then shoots at them. I've figured out how to prompt the shooting, but the targeting leaves much to be desired. Quite simply, how should I write a script causing the turret to realize the existence and location of enemies within its range? I've figured out that there may be an option related to a rotational, radar-like ray, but I cannot figure out how to execute this. Could someone please either instruct me on how to carry this out or point me in another direction?