In the Dragonball Series there are three types of fusion. Fusion is when is when two people of commonly the same power level or same heart come together and form a stronger character. Fusion is easily messed up and takes two or three times to get right.

FUSION DANCE
The fusion dance is the most common form of fusion. The fusion last for up to thirty minutes and can be done easily after mastered for the first time. Two characters do a dance while shouting fusion. They then touch each others fingers and make a new person. The person has the personality of one person and the strength of the other. When the people fuse and mess up they form a fat fused person. Fused Characters are Goku + Vegeta = Gogeta. Goten + Trunks = Gotenks

PORTORA EARINGS
To do this fusion, the characters must put on the portora earings. They fly in the air and fuse into one. The only people to fuse are Vegeta + Goku = Veggeto.

FUSION OF THE HEART
Not much is known about this fusion. Twonameks can fuse if the have the same care in the heart.