The Spirit Bomb is an ancient technique used by Goku which he learned from King Kai. The Spirit Bomb is said to be one of the strongest techniques ever created. The attack is used by absorbing the energy of anything living, and willing to give up energy. Goku uses this attack many times in stressful situations sort of as a last hope. At first Goku`s spirit bomb is about the size of a basketball. Then it becomes the size of a small planet.
The first Spirit Bomb Goku used was against Vegeta. This Spirit Bomb was created by most of the Earths energy.
This attack was thrown by Krillin due to Goku being weakend from Vegeta. This attack was not enough to stop Vegeta, most likely due to being at half power.
Large Spirit Bomb
The large spirit bomb is a Spirit Bomb formed from the energy of the whole galaxy (besides the people). The only time it was used, was against Frieza after Goku ran out of living options. When it was thrown, Frieza suffered many injuries, but he survived it miraclulously.
Super Spirit Bomb
The Super Spirit Bomb is the attack used by Goku, to destroy Kid Buu. When Goku th
rew it at Kid Buu, he started to push the move back! Goku was out of energy so he knew the Bomb wasn't powerful enough to obliterate Kid Buu. So Dende used the Namekian Dragon Balls to restore Goku's energy. Goku then went Super Saiyan and sent the Spirit Bomb flying at Kid Buu! Obliterating him once and for all.
Universal Spirit Bomb
The Universal Spirit is used by gathering all the energy of the universe (including people). The only time it's used is
by Goku to defeat Omega Shenron.