Iso is the light sensitivity so if it is high the photo will be lighter and if it is a low sensitivity it will be darker.
Aperture is the amount of light given to the photo you have taken so if it is high then it will add a lot of light (brightness). So you have taken a photo it will make your photo look brighter and if it is really high it will make your photo almost look white or look completely white and if you have a low aperture it will make your photo look dark and gloomy.
Shutter speed is when you take a photo and inside the camera there is a device when you take the phot it will shut fast or slow you have to adjust how you want it shut fast or slow so if you take a slow photo of a motorbike moving it will catch it 1 or 2 seconds late but if it is a fast shutter speed it will catch it fast and blur the background if you set aperture and iso correctly.
Manual mode is when you do everything by yourself set focus set the aperture set the iso
automatic is when the the focus is already set for you aperture and iso aswell so everything done for you don't have to change anything.