Behavior of the '*' operator in Array in Ruby

I am a newbie in Ruby. Please explain how the * operator works in this case.

arr = [1,2,3]
p arr
arr = *[1,2,3]
p arr
*arr = [1,2,3]
p arr
arr = [1,2,3]
p *arr

OUTPUT

[1,2,3]

[1,2,3]

[1,2,3]

1

2

3

What is happening in the last case ? Is it behaving as a iterator ? Can anyone give an example as to how to use it ? Also why it has no effect in the second and third case ?