ISO is all about a cameras sensitivity to light, more specifically the cameras image sensors sensitivity to light. Take a look at the chart below, it gives a summary of how the ISO scale works.
The higher the number, the greater your ability to take photos in low light becomes and vice versa. The drawback here is that higher ratings can produce a grainy result in your photograph know as 'noise' so as a pro tip you want to use the lowest ISO number you can to help reduce the noise in a photo.
Aperture is the opening in the cameras lens that lets the light in and how big or small that hole may be. Its handy to think of this in a similar way to your eyes. Have you ever found yourself squinting to make something appear more focused? This is the same as how a camera works - the smaller the opening the more focused the image will be. When you are looking at the description for a camera lens it will say something along the lines of F2.8 - F5.6, this refers to that lenses aperture capabilities. Have a look over the chart below, hopefully it will help to understand the aperture scale a little bit more. Further below is an example of what the same image can look like with different aperture settings.
Inside of your camera, in front of the camera sensor there is a sort of curtain that is designed to block light getting to the sensor. When you press the button (also known as the "shutter button") to take a photo this then opens the curtain allowing the sensor to collect light and closes again once the photo has been captured. The Shutter Speed is the length of time the camera shutter is open. If you a using a "long" shutter speed then any motion in the photo will be blurred, the opposite is also true when using a "short" shutter speed can freeze motion. Experimenting with the shutter speed can create some really cool effects in your photography so it is worth playing around. Have a look at the image below for a visual representation of shutter speed.