Hello Teja,
The simple and standard format: (to be typed on the company letterhead)
TO WHOMSOEVER IT MAY CONCERN
This is to certify that Mr./Ms. [Name] S/D/W of [Address] residing at [Location] was employed with us as [Designation] in the [Department] from [Start Date] to [End Date].
During their tenure with us, we found them [comments i.e., sincere and hardworking or any other comments as per the employee's performance], and also their character and conduct were found to be good/very good/exemplary.
We wish them all the very best in their future endeavors.
For [Company Name]
Authorized Signatory
With regards,
Anabayan