Fibonacci Sequence is a sequence of numbers in which you get the next number of the sequence by getting the sum of the two numbers prior to it. 

The Fibonacci sequence was actually first described by the mathematicians in India over 1300 years ago, before being brought to the west by a mathematician Leonardo of Pisa (1170-1250), or most commonly known as "Fibonacci", where he introduced the concept through his book Liber Abaci in 1202, by visualizing the concept using rabbits and how they multiply (see image of leonardo of pisa, on the left)

Golden Ratio also known as the "divine ratio", and the spiral and numbers may seem intimidating at first, however it can be seen as the visual representation of the Fibonacci sequence.