Question:
Can anyone explain how to make water purification? (this is only for a simple science project)?

I've heard/read some methods of water purification using charcoal and sand but can anyone explain how to really use them as water purifiers?

Answer: You can use sand as a filter for particulate impurities. Wash the sand, then put it into a container with a hole at the bottom. Pour the water into the sand, let it run through the sand and out the hole at the bottom, and anything relatively large that was floating in the water will be trapped by the sand.

The charcoal works much the same way, except that the carbon in the charcoal tends to latch onto chemical impurities rather than physical ones.

If you're not married to the sand/charcoal filter idea, there is another approach. Put the dirty water into an open-topped container of some kind and stretch some clear plastic wrap over the top. Tilt the container slightly towards one side and let the plastic wrap trail off over the downhill edge. It's helpful if you can put a small notch in the edge of the container and "bunch" the plastic wrap up to make a sort of inverted trough in it leading out through the notch. Put the container in the sun and wait. Sunlight will evaporate the water, which will collect on the plastic wrap. The trough and gravity will cause it to run out the bottom, and you can collect it in another container by letting it run off the plastic wrap.