Namekian Fusion
This type of fusion can only be performed by two Nameks. With this type of fusion, the energy and power level of one fighter are absorbed into another fighter. One of the fighter, in other words, is the base and after the fusion, the character who is the base looks the same. To fuse the Namek simply places their hand on the others chest.
Namekian Fusion Occurrences:
During the fight with Frieza, Piccolo is wished to the planet, Namek. As he makes his way to where the others are confronting Frieza, he comes across Nail, who was beaten severally by the evil villain. Nail asks Piccolo to fuse with him but Piccolo is skeptical. Finally, Piccolo agrees and places his hand on Nail’s chest. The fusion takes place and Nail is fused with Piccolo. Piccolo looks the same but now has Nail’s power level and fighting abilities. Dende also recognizes Nail’s mannerisms in Piccolo.

During the Android saga, Piccolo realizes that the Z fighters have little chance to defeat the androids on their own due to Goku’s heart disease. Piccolo goes to Kami and asks him to fuse so that they can have a chance against the threat. Kami waits to do this but changes his mind after observing Cell’s appearance and terrorization of the planet. The two fuse and Piccolo increases his strength immensely sense Kami is a powerful god.

Fusion Dance
This type of fusion was taught to Goku in the afterlife. It is a complicated dance that the fighters have to perform perfectly. If the fighters do not perform the dance exactly, then the body of the fighter will be distorted into another, less powerful form. Furthermore, the fighters also must be about the same size and weight and must be almost equal in power level. As the fighters perform the dance they say the word, “Fusion.” The fighters are now fused but must move quickly to defeat their enemy due to the Fusion only lasting for 30 minutes. After that time, the two characters return to normal. The clothing is a vest with padding along the neck and arms with loose fitting pants similar to Goku’s with a long belt.
Fusion Occurrences:
During the fight with Janemba, Goku must convince Vegeta to fuse with him. He teaches Vegeta the dance quickly and they perform it for the first time. Unfortunately, Vegeta fails to point his finger the correct way and the fusion is altered. The result of this is Fat Gogeta. Fat Gogeta gets kicked around by Janemba and the two have to wait for the fusion to wear off. Luckily, Pickahan, another fighter, distracts Janemba long enough for the two to fuse again. This time they do it correctly and the result is Gogeta.

Piccolo teaches Goten and Trunks to do the Fusion dance during the Buu Saga. They eventually get the dance right and form Gotenks.

Potera Earrings
This process results in a permanent fusion. To achieve this fusion, two fighters must wear Kaioshin’s earrings. These are the Potera Earrings. The fighters must each wear one earring in opposite ears. As soon as the earring are in place the two characters are pulled together and a new character is created. Unlike the Fusion dance, the two fighters do not have to be close in body size or power level. When the fighters fuse, their clothing changes to a combination of the two fighters wardrobe.
Potera Earring Occurrences
Kaio-shin and Kibito fuse for the fight with Majiin Buu and become Kibito-Shin.

During the fight with Buu, Goku was originally suppose to fuse with Gohan using the Potera Earrings. Gohan dropped the earring when Buu absorbed him and Vegeta picked it up. Goku has to convince Vegeta to fuse with him. Finally, Vegeta agreed and the two were pulled together and Vegetto was formed. Vegetto then entered Buu to save all those that had been absorbed by him. When he entered Buu’s body, the fusion was cancelled out and Vegeta and Goku returned to their normal individual forms.