When God began His creation, the world was dark and empty. Just like a blank page...

God said "there be light", and there was light. Then the darkness was separated from light. Just like when you turn on the light of a dark room. 

He called light, Day...

... and the dark, Night. The day and Night become the first day. 

The second day, God worked separating the waters from the expanse...

...and He called the expanse, Sky. 

God piled up the waters into one area, and then land appeared. He called land, Earth and the waters, Sea. 

He said "let the earth produce trees, plants and fruits. Everything was good. This was the third day. 

The fourth day, God made two greater lights to shine the earth. One big light during the day...