Super Saiyan- Goku is the first one to reach this state. In this state the Saiyan gets golden colored hair,blue-green eyes and a largely increased power level. This state is triggered by pain,loss,sadness any of those. Goku reached it because the death of Krillin angered him.
USSJ-Ultimate Super Saiyajin- Trunks, Goku, and Vegeta all reach this state. In this form they retain the same hair and eye traits as a normal Super Saiyan but in this form the individualís muscles get a lot larger and their speed increases immensely though their strength increases. Trunks and Vegeta both tried to use this form in the fights against Cell, though Vegeta didnít notice the downfall to this form, Goku did and Trunks finally did after discovering that he couldnít catch Cell. Goku noticed the downfall to the form while he was in the Hyperbolic Time Chamber, I believe Brolly reaches this state as well.
Super Saiyajin 2-This form was reached by Goku,Gohan,Vegeta and I think Trunks may have,not sure about Goten.In this form they look almost the exact same as a Super Saiyan except their hair is a bit more spikier and has more of a white tint to it.They're power level also increases even more than USSJ and SSJ.
Super Saiyajin 3-This form is reached by Goku only.In this form Goku lost his eye brow hair and the hair on his head grew longer,reaching about to his feet.His power was increased immensley though they don't get any bigger muscle wise.Vegeta skipped this level due to the Brute Ray that he had Bulma build while he was under the influence of Baby.
Golden Oozaru-The primal state of SSj4.This is reached by Vegeta and Goku.In this form they turn into a giant monkey,just like their normal monkey form except they are golden colored and way stronger.Goku and Vegeta had to get control of their primal state of this mind to be able to go into SSj4.
Super Saiyajin 4-The controlled form of the Golden Oozaru and the most powerful of the Super Saiyajin forms.This form is reached by Goku and Vegeta.In this form they gain red fur over their body and they retain their black hair color except their hair is a little longer and they get a red tail.Now some,like me,believe this is the true Super Saiyajin form as in one of the episodes when Vegeta is talking about the legendary Super Saiyajin in shows a giant golden monkey,and SSj4 is the controlled state of golden oozaru.And they retain their human like form and it is sort of mixed with the monkey part of them,giving the impression of half human-half monkey,so yeah.