Hi Prema
This is a wonderful opportunity for you to overcome your fears, don't worry about anything. just prepare yourself to the fullest.
get the summary of the trainers ( educational qualifications, achivements, highlights etc)
Prepare the welcome speech and keep it handy with you on a peice of paper
learn all the details of the trainers which you will be speaking by heart.
On the day of speech, speak to the crowd as if you are speaking among social circle, but make sure you are professional and polite.
Convey the information of the trainers in such a way as if you knew them. speak from the heart, appreciate the achievements as you truly would.
Maintain eye contact in all directions slowly and steadily. never let go the smile off your face.
keep the welcome speech small.
If you are really nervous, you can use the mike podium, stand behind the podium and speak, carry the paper of speech with you.
if you cant use the podium, then get yourself very familiar with the stage from which you will speak, go on the platform and rehearse the speech and style again n again, you will start gettin confidence.
be excited about it, dont fear it. and public speaking is a matter of great effort, audience respects those who speak. so dont worry, even if you goof up, its just a funny incident in your life worth remembering.