That means, only Allah could have made mankind and the earth, moon, sun and stars. Allah is the only One who created all these. Of course, you know that many things on earth just work by themselves. For example, when you put seeds in the earth and wait a few months, plants will grow out of them. You may say that the seeds can be taken from other plants, and you would be right.
Earth is made out of fine particles of sand, minerals, salts and other materials.
The plants need sunshine in order to shoot out from the ground. We also need the day and night so that we can count how many days it takes for the plants to grow. As we have already said, it is easy to put the seeds in the earth and wait till the plants grow out of it, but nobody can make all the things that are needed to make it work. No man can make earth and air, light and water, or the day and the night. It is exactly the same with all other things.