"I am this boy."
Translation:Я этот мальчик.
There is a sticky topic in the Discussions about that.
Этот (эта, это, эти and other forms) is an adjectival pronoun which is used before noun. It agrees with the gernder, number and case of the noun it decribes. If you can replace it with "my", "your", it is a good sign you need this word.
- if you are talking about objects mentioned before, sometimes this demostrative adjective can be used without a noun, similar to how in English you can use "this one" without specifying what "one" is—provided that it is clear from the context.
At the beginning of "This is" or "These are" sentences you always use "это". The form does not depend on what follows.In English you would probably need to use "mine" and "yours" in this position: "my" or "your" will feel wrong.
OK, maybe I'm wrong, but I guess that the easiest trick to make the difference is asking yourself which is the subject.
I am this boy
"Boy" is the subject. So you have to use Этот (эта, это, эти if the genre it's different).
In other phrase:
This is a boy.
"This" is the subject. So it always has to be translated as Это, it doesn't matter if it's raining or storming.
I promise I get crazy to get this conclusion.