Aperture is referred to the lens diaphragm opening inside a photographic lens. The size of the diaphragm opening in a camera lens regulates amount of light passes through onto the camera the moment when the shutter curtain in camera opens during an exposure process.

It very important in photographic element called "depth of field"
The bigger the apertures used, the zone of sharpness is shallower or vice versa i.e. smaller aperture used will has extended depth of field..

Aperture size is usually calibrated in f-numbers or f-stops

Adjust the aperture to change range that is in focus and background blur
Smaller F -   Isolate subject - image
Larger F -  Focuses on all

Larger F Shooting the depth of the scenery.Narrowing down the aperture widens the range that is in focus. (Depth of field becomes deeper)

ISO is fundamentally the sensitivity at which your cameras sensor reacts to the light when you open the shutter.

ISO is measured in a scale (On standard digital cameras) called ISO. ISO is the number indicating a digital camera sensors sensitivity to light, the higher the sensitivity, the less light is needed to make an exposure.

But the problem when using high ISO is the picture tend to be grainy, thus lower ISO is perfect if you want crispy and clear image.

For me, taking picture in dim light with high ISO is better than using flash.

I’m still learning on how to get the perfect ISO level.
So I decided to test capture using ISO early this morning. It was 7 am and the street lights was still on!

So lets the photos do the talking :)