In 1658, and Irish bishop named James Ussher reconstructed a chronology of the Universe based on the information in the Bible (considered the standard method at the time). His calculations placed the date of creation on 23 October, 4004 BC.
Modern scientists like Charles Darwin suggested a very different possibility for the development of life on Earth. His theories suggested that the Universe must be far older than anyone had previously considered. Natural Selection and Plate Tectonics both involve very gradual changes which occurred over millions or billions of years.
Most scientists now believe that the Universe began with a Big Bang. Most people are somewhat familiar with this idea. All matter and energy was once compressed into an infinitely small dot called a singularity. Intense heat and pressure caused a massive explosion which cooled and expanded to form the Heaven and the Earth.
Time and Space were created along with the Universe, so there was no "before" the Big Bang. Scientists think they know what happened after the Big Bang, except for the first millionth of a second. During this period, called Planck Time, fundamental forces and the laws of physics were still forming.
The temperature at the Big Bang was roughly ten trillion trillion times hotter than the core of our Sun.
The most important evidence suggesting the Big Bang was discovered by Edwin Hubble. Using modern telescopes, he noticed that other galaxies seemed to be moving away from Earth. This is true no matter what direction you look in: they're all moving away from us, suggesting that the Universe is expanding. Extrapolating backward over billions of years, he theorized that all matter and energy must have once been contained in a very tiny space.
Astronomers believe that the Universe came into being between 12 and 15 billion years ago. A small amount of tv static is actually created by radiation left over from the Big Bang, which has taken countless billions of years to reach Earth.
Perhaps a billion years after the instant of creation, gas clouds formed giving birth to the first stars. Five billion years ago our Sun was born and the Solar System began forming. Earth became a planet about four and a half billion years ago.
There are an awful lot of good books on astronomy and the origins of the Universe. Two of the best are The Short History of Nearly Everything, by Bill Bryson and Don't Know Much About the Universe, by Kenneth C. Davis. Both do an incredible job of explaining very complicated material in a way that's interesting and easy to follow.