any one plz tell me the basics of sending AT commands to microcontroller from GSM kit
Why do you title this "doubts"?
What have you heard and/or read that you doubt? What is it, exactly, that you doubt about it?
The basics of AT Commands have absolutely nothing whatsoever to do with microcontrollers or programming.
The basics of AT Commands involve:
1. Understanding what AT Commands your particular "GSM Kit" supports;
2. Choosing which of those commands will be necessary to support your intended application;
3. Understanding what responses to expect when you send these commands to the "GSM Kit" - including error and/or failure indications.
Again, none of that has anything to do with microcontrollers or programming - it just requires you to study the documentation for your "GSM Kit", and to think.
As an aid to your study & thinking, you could try:
A. googling - there is loads of information available on this!
B. sending commands "manually" and observing the responses - eg, using hyperterminal.