Use Get Axis to get the player input (you can test axis input with the cursor keys and WASD as well as a joypad) and apply the input as a rotation around Y (or whatever axis you need to rotate around).
In the attached screenshot, the rotation is applied "per second" so it's frame rate independent. The input multiplier controls the max speed of rotation - in this case 90 degrees per second.
Unity's input manager gives you some nice smoothing on the inputs, so you get smooth rotation.