how to create api and use creating Web API like Twitter API

Hi,
 
I am developing a project where user will come and write their opinions and comments on some employers with their scores such as good, bad, excellent, etc. and this data needs to be shown on all the clients websites with those actual data with the scores e.g. good, bad, excellent, etc. for example I have got 100 employers in the database and all the employees of those 100 companies will come and write their scores on a single website and then my role is to show the real data related to that particular company to their website. And I am not allowed to show the x company;s data on y company's website. Meaning thereby, XYZ-employer should get the real data related to XYZ employer and not of the ABC employer and ABC employer should get only ABC related data.
 
So how would I perform that functionality? what are the possible alternatives or the different different methods for achieving that.
 
Will it be like creating Web API like Twitter API or Facebook API? which shows the likes or tweets related to that login account.
 
Please suggest ASAP. Thanks in advance.