Potara Earrings-This fusion is when there are two earrings. Someone puts one of the earrings on one of their ears and you put the other one on the opposite ear. The two powers don't have to be equal. The bad thing is if your ear isn't pierced, it's going to hurt. The good thing is it adds the two powers together but adds even more power than the fusion. If you are fused with someone using the Potara Earrings, you are permanently fused unless you are forced apart.
Gotenks-Gotenks is the fusion of Goten and Trunks. He is formed to stop Evil Majin Buu. He is a very character, but he was cocky because he thought he could easily defeat Buu. Buu beats him easily. Gotenks gets a second chance to defeat Buu, but again was cocky and he was absorbed making Buu even stronger.
Gogeta-Gogeta is the fusion of Goku and Vegeta. Gogeta never appeared in the DBZ series. He only appeared in DBZ movie 12 to defeat Janemba from taking over HFIL. The first time they did the fusion , Vegeta messed up and made a fist. This caused the fusion to mess up forming Fat Gogeta. Fat Gogeta kept farting on Janemba(think of how he felt).After being kicked around by Janemba for 30 minutes, they unfused. After waiting an hour, the did the fusion again and easily defeated Janemba.
Vegeto-Vegeto is formed when Goku and Vegeta put the Potara Earrings on. The earrings are made so that fusion will last forever. Vegeto is the most powerful fused Saiyan. Vegeto went into the pores of Buu to rescue their friends who had been absorbed, including Fat Buu. When he did this, Buu was turned to his regular form, but Vegeto became unfused. Piccolo, Nail, and Kami are only fused forever (not by the Potara Earrings) by using a special Namekian fusion technique.