The first level a Saiyajin can reach. It increases the Saiyajin's power, speed, etc. Goku first reached this form when Frieza killed Krillin. The anger was so great that is sparked the transformation. Emotion is what helps trigger this stage. Vegeta says that the emotions can be good or evil. The hair pikes up and turns gold. A slight muscle increase. Eyes turn green and an aura of gold energy appears.
When Gohan's anger exploded, It triggered the Super Saiyajin 2 transformation. This stage makes the Saiyajin faster, more powerful, and very deadly. The hair pikes up alot, and the golden aura now has electric sparks flowng through it. Super Saiyajin 2 was reached by Goku and Vegeta in the Buu saga,
Goku first reached this level during the Buu saga. Unlike the previous forms, This stage is triggered by intensive training. This form is the last of the normal SSJ levels in DBZ.
In this stage, you become very bulky. Your hair grows to your lower back. Your eyebrows disapear. This form is very powerful. The only people who reached this stage were Goku and Gotenks
The last of the SSJ forms and the most powerful. Goku, Vegeta, and Gogeta were the only ones to reach it. In this stage your hair stays black but grows to the back of your upper back. Your body becomes covered with red fur. To reach this stage, The Saiyajin MUST have a tail. Then you must have controlled the golden oozaru stage. When you do the transformation will occur. This stage is believed to be the true SSJ by some, and not by others.