HR Query For Small Scale Industry Workers

Hello
I own a small scale Cattle feed industry with no hr department in it. All my employees work without any Joining/Offer/Appoint letters yet. But, now I would like to issue them an official letters on behalf of my proprietorship firm.
My query is what should I provide them especially for my old staff work in sales and operations department. Also letter with particular formats will be very helpful.
Appreciate very much.

Dear Industrialist,
It does not matter what type of standardised format you use for issue of appointment letters. first of all are you a registered concern anywhere? like CBDT, SALES TAX, ESI, EPF, Labour Out sourcing etc? If yes, then it is mandatory for you to maintain the decorum. If you are a small player, then i think your honesty towards your organisation and worker's welfare would bring you growth, contentment and profitability. so, if you are concerned about labour interests, please issue everybody an appointment letter as they deserve it.