Universe is nothing but a combination of various elements such as planets, stars and galaxies. The start of the Universe is still on research and till now there are a total of 4 theories which depict about the birth of the Universe. So it is can be called that a universe is a combination of energy and matter. Universe is a very vast thing and its size cannot be defined but we have observed about 47 billion light years approx. equal to 4.40 X 10^26 meters from the earth.
The shape of the universe includes local geometry and global geometry, which can be found in the observable universe. The cosmologists are working on the shape of the universe. The cosmologists work with a space like slice of the space time which is known as commoving coordinates. It is in the shape of a backward light cone.