You can then display this in one of two typical ways.
The first way is by holding your hand out in front of you, with the index and pinky fingers pointing upward and the other fingers and thumb pointing away from you.
The second is by holding your hand extended above your head, with the index and pinky fingers pointing upward and the other fingers and thumb pointing away from you, and then waving your hand forward and back, forward and back, over and over again in a rapid, fluid motion (this is actually the "throw" part of the phrase) - at a rock music concert, this motion is typically performed to the beat or rhythm of the music or lyrics.
"Throwing the goat" originated at early heavy metal rock concerts, and originally symbolize the horns of The Goat, i.e. the Devil or Satan. It has since lost that meaning to some degree. It now is often used to denote that something, someone or something someone has said, is cool. In a similar way, it often means something along the lines of rock on! Etc.