Estar muy verde
 

May anyone tell me if there is an equivalent idiom in english?

In spanish we say "estar muy verde" when somebody is just starting to learn anything. Estoy aprendiendo inglés, pero todavía estoy muy verde.

We have the same idiom (to be (very) green (at something)), but we would probably choose other ways to say the sentence you wrote.

Here are a few different ways to say the same thing:
I'm learning English, but I'm still a little green (at it).
..., but I'm still (just) a greenie.
..., but I'm still (just) a newbie. -or- ..., but I'm still new at it.
..., but I'm still (just) a tadpole.

..., but I'm still (just) beginning. -or- ..., but I'm just starting.
..., but I'm still in the beginning stages. -or- I'm just beginning to learn English.

Thank you, Rusty.

But, is it possible that the idiom is only used in America? I ask it because I used the idiom literally translated from spanish with my conversation teacher, and he didn't understand it. Could it be because he is Irish?

OT: Why is incorrect the use of May in this sentence? Thanks (por anticipado?)

The word 'may' may not be used in that spot. If you're asking for help, you use 'could' or 'would'. The former is a form of to be able to (poder); the latter, the conditional tense.

These are basically equivalent pleas for help:
Could someone help me?
Would someone help me?

If you're offering help:
May I help you?
Could I help you?
But not:
Would I help you?

I wouldn't think that being green (being new at something) is entirely American. Perhaps your teacher just didn't understand. There are other sayings that use the word green, too. More so lately, in America you're green if you're depending less on fossil fuels. (Es ecologista.) :)

Being "green" is still used a lot in the law-enforcement / military culture, though I think it's a term that the younger culture in America may be less and less familiar with. As for its use in other countries, I couldn't say. Idioms can be highly regional.

Myself, I'm partial to the term "green-horn", which means the exact same thing (but is more "cowboy" speak). The fact that it's also part of one of my favorite lines from "The Simpsons" helps.

I love the word "greenhorn". It is so ... "western":p

Exactamente!

Del mismo modo, ¿Puedes dices alguien es azúl?

Se dice que alguien está triste o deprimido.

¿Cuando tú hablas en general, tú usas "el/ella/Ud." en vez de "tú"?

Cuando hablamos en general, se usa el se impersonal.
Where we use 'people say, they say, or one says', Spanish uses the impersonal se construct.