When a Saiyan goes Super Saiyan (SSj) this means he got really mad suddenly and had a big rush of energy. Like Goku against Frieza aka Freezer or Freeza. Later on after you can control whether you want to go Super Saiyan against an enemy or not.
Super Saiya-jin, SSj
This Saiyan had a sudden rush of energy that pushed him over the limit. Your muscle mass increases greatly and his hair turns yellow plus the eyes go green. Your power level increases tremendously. This is hard to control because of so much anger and power. Goku was the first to ever go Super Saiya-jin when Kuririn dies against Frieza.
People that have gone Super Saiya-jin: Goku, Vegeta, Trunks, Gohan, Goten, Gogeta, Vegetto, Gotenks, Brolly.
Ultra Super Saiya-jin, USSJ
This stage increases muscle mass tremendously. Your hair spikes up more than Super Saiya-jin and is still yellow. Your eyes stay green but has a meaner look in them. Your strenght increases greatly but everything else decreases. Vegeta is the first one to reach this level when he came out of the room of spirit and time and powered up against 2nd stage Cell.
People that have gone Ultra Super Saiya-jin: Vegeta, Future Trunks, Goku, Brolly.
Super Saiya-jin Level 2, SSj2
This stage increases muscle mass as well as the first stage. Your hair is still yellow but it grows longer and the eyes stay green. Your power increases greater than Super Saiya-jin or Ultra Super Saiya-jin. Gohan was the first one to ever go Super Saiya-jin 2 against Cell when he saw his friends get beat up and #16 dies.
People that have gone Super Saiya-jin 2: Gohan, Goku, Vegeta, Gotenks, Vegetto, Brolly, Gogeta.
Super Saiya-jin Level 3, SSj3
This stage pumps your muscles up a ton. Your hair turns yellow like always but it grows down to ur ass. Your eyes are still green but you lose your eyebrows. You look more menacing and lean. Everything increases greatly. Goku was the first one to ever turn Super Saiya-jin 3 when fighting Buu.
People that have gone Super Saiya-jin 3: Goku, Gotenks.
Super Saiya-jin Level 4, SSj4
Big chances happen in this stage. Your muscle mass grows more than any level. Your hair grows to your ass but the color is black. You also get fur and u dont have green eyes. You look bad-ass and mean. You need a tail to get to this level. This tail helps you go Golden Oozaru form (King Kong style heh). Your power level is ungodly and no one can defeat you, unless it is Super 17 <smirks>. Goku was the first to reach this stage when his tail was out and he became Golden Oozaru, he converted all his anger and strenght to Super Saiya-jin 4 against Bebi Vegeta.
People that have gone Super Saiya-jin 4: Goku and Vegeta.
The Namekian fusion is diferent than any other fusion because it is permanent. Only Nameks can do it. If you fuse and you want the fusion to be with you body then your the one that puts the hand on the other Namekian's chest and absorb it. The other Namekian has to power up to his full in order to gain more power.
People that have done the Namekian Fusion: Piccolo, Kami, Nail.
Android Fusion
In an Android fusion one android absorbs the other Android. It doesn't matter how many Androids fuse together. Is a fusion made by absorbtion or combination. In movie number 7, Android 13 absorbs Android 14 and 15's chips and becomes Super 13. That is an example of absorbtion. In DragonBallGt, Android 17 and Artificial 17 combine into one because they were identical and so they became Super 17. An Android fusion is also forever.
People that have done the Android Fusion: Android 17, Artificial 17, Android 13, Android 14, Android 15.
Potarra Earings Fusion and Fusion Dance Fusion
A normal fusion is created by the Potarra Earings or Fusion Dance. I don't know if this is true but only Saiyans can fuse by Potarra Earings or Fusion Dance. The Potarra Earings let's you fuse forever as long as you have the earings or they work. When Goku and Vegeta fused with the Potarra Earings they created Vegetto. The earings somehow got damaged so they couldn't fuse into Vegettto again to fight Buu. The Fusion Dance is a dance that you have to get everything perfect or the fusion will go wrong. It only works for 30 minutes so you have to get the job done while your fused. You can fuse once again after the 30 minutes but it's a pain in the ass. Goten and Trunks do the Fusion Dance in the Buu saga but they are so cocky that they didn't win. In movie 12 Goku and Vegeta did the Fusion Dance and turned into Fat Gogeta because Vegeta messed up. After the 30 minutes they tried it again and did the Fusion Dance correctly creating Gogeta and easily killing Janemba.
People that have done the Potarra Earing Fusion: Goku and Vegeta (Creates Vegetto).
People that have done the Fusion Dance Fusion: Goku and Vegeta (Creates Gogeta) , Goten and Trunks (Creates Gotenks).