[QUOTE=nisrin;816794]Hello everyone, I am a new teacher and I have a problem in teaching my students how to use "what", "when" and "who" to form questions. I am a little bit confused. They can't write full statements, their English level is too low according to their grade. (I'm not sure what you mean here - perhaps "considering the school grade they are in, their level is low"?)[/QUOTE]
If your students can't yet write full sentences then it is perhaps a little early to be trying to teach them how to convert a statement into an interrogative. I think you probably need to concentrate on helping them to write full sentences first - you and they can worry about the interrogative in the future.
I have a query though - it is only "what", "when" and "who" that you are having problems with? No problems with "why" or "how"?
Please see my amendments to your post. As an English teacher, I'm sure you understand the importance of not only speaking correct English, but writing it correctly too. Please note that "I am" is two words, we always put a space after a comma and a full stop and that "English" must always be written with an initial capital letter.