Yell x Scream x Shout: Qual a diferença?

Hellow people, sorry I didn't understand when can I use Yell or Scream.

As palavras "scream" "shout" e "yell" são sinônimas? Se não, qual seria a diferença entre elas? Existe alguma regrinha para usa-las?

A baby screams. An adult can also scream, but usually out of fear, frustration, or other uncontrolled emotions.

Shouting and yelling are very similar, and I don't know if I can give a clear difference. In describing a fight between two people, I would probably say "yelling". But if people are talking loudly, but not fighting, I would say "shouting".

Anyway, that's my explanation. This is actually a common question and you can find many responses to this question on Yahoo Answers as well.

Hi there, complementando

You can learn a lot from online dictonaries, OK!

SHOUT: to say something in a loud voice; to speak loudly/angrily to somebody.
Stop shouting and listen!
I shouted for help but nobody came.
Then he started shouting and swearing at her.
She shouted at him to shut the gate.
He shouted that he couldn't swim.

YELL: to shout loudly, for example because you are angry, excited, frightened or in pain.
He yelled at the other driver.
She yelled at the child to get down from the wall.
They yelled with excitement.
She yelled out in pain.
The crowd yelled encouragement at the players.
He yelled out her name.
Source: Oxford Learner"s Dictionary

They are almost the same, in some situations like "pain" you're going to say "yell", not "shout".
Angrily you yell or shout, but when you say things aloud because you're excited, angry, so on... it is more common to describe that as shout.
In everyday conversation I would say "shout" seems to be more common.
See the preposition used: Shout at somebody.
As for "scream" erikspen have already explained very clearly.

Cheers!