Honestly, forget the post-processing bit if you're just starting out.
The rest is pretty simple if you have a tripod (kinda necessary for long exposures, to avoid camera shake).
Just set your camera on a tripod (or a still surface). Set to delayed trigger (2 second delay or 10 second delay, to avoid shaking the camera with your finger).
Then point it at a nighttime scene.
I shoot in Av mode (Aperture Priority mode) and therefore, I set the aperture to f11 or so (for maximum depth of field, ie, a sharp image all the way from close to far) and let the camera pick the appropriate shutter speed.
If you're shooting at night, said shutter speed will inevitably be quite long to let in enough light (mine worked out to 30 seconds by the camera) which will blur the cars or any movement happening in the frame.
Sorry if that is all pretty obvious to you. Otherwise, happy to help.
when im in AP, if i turn the dial to make the F go up, it brings the ISO up as well....how do i stop that?