Hi Pallavi,
Meeting 200 people in groups won't be that difficult if all of them are available within the same premises. I believe you need to be an efficient communicator, given that your boss has entrusted you with this assignment. From your post, I gather you may be a bit nervous about the enormity of the task, or you may not be an extrovert by nature to reach out to people and explain things in a language that may not necessarily be politically or grammatically correct. However, if your audience can clearly understand what you want them to grasp, your purpose will be served.
To begin with, ensure that you yourself have a very clear understanding of the policies and procedures of every subject that you need to convey to your coworkers, so that during the interaction, you can clear all the doubts of your audience without feeling stressed.
Once you are confident about the subject, chalk out a schedule over a 10-15 working day period, issue a general notice for people to attend the meeting on the respective date. The meeting should not exceed a duration of 30-45 minutes. If your organization feels that you are utilizing too many man-hours by conducting these meetings, you can take the management into confidence and ask the involved people to attend the meeting outside working hours. I believe nobody will object to coming early or leaving late once.
Ensure that all the material you need to explain is provided as a booklet to your audience after the meeting. Additionally, paste the material in a book and take the signature of the person attending the meeting, stating that the policy and procedure mentioned in this book has been explained to them, and they have read and understood it entirely.
I hope this will not only clear you as you will have evidence that you have explained the policy and procedure to your coworkers but also provide them with a backup to reread the material in case of any doubts.
Don't worry about the task, just do it, because once you start, you can finish it off. Just do it. Ho Jayega.