Fusion Dance: Start by pointing arms away from your partner. Slide your arms above your head, and squat your knees. Then point your arms toward your partner and your inner knee away. Then put your feet apart, bend to the side, and touch index fingers with your partner. If done correctly, a powerful fusion should occur, but if done inccorectly, fusion will be very weak, in either a fat or skinny form.

Succesfull Fusions: Gotenks-From Buu Saga and Movies 12 and 13, formed by the fusion of Goten and Trunks. Formed to fight Buu, and eventually went Super Saiyan 3 to escape from the Room of Spirit and Time. In Movie 12, fused to fight Hitler's army. In Movie 13, fused to fight Hindergaren.
Gogeta-Gogeta is formed in Movie 12, "Rebirth of Fusion" to battle Janemba. Gogeta easily overpowers Janemba, and kills him.

Unsuccesfull Fusions: Fat Gogeta-Vegeta neglected to put his index finger out, resulting in the fat version of Gogeta. Only usefull attack was his farts.
Fat and Skinny Gotenks-While learing the fusion dance, performed it many times wrong in the Room of Spirit and Time.

Patorra Earrings When two fighters of similar power level and size each put an earring on, the combine to make an ultra strong fighter whose power exceeds that of a fusion dance fighter.
Vegetto-When Gohan was absorbed by Buu, Goku was forced to fuse with Vegeta to form Vegetto. Ultra strong and hyper fast, Vegetto beat the crap out of Buu, but went inside Buu to save everyone, and the "permanent" fusion somehow wore off.