A Certificate presents an organization in an official digital form. This is same to an electronic identity card which serves the purpose of Identifying the owner of the certificate. This is done with authenticating the owner through trusted 3rd parties named the certificate authorities (CA) e.g. Verisign etc. The Authorities digitally signs these certificates. When the user represents the certificate the recipient checks it by using the digital signature.
Distributing the owner's public key to his/her users (or recipients of the message).The server certificates let visitors to your website interchange personal information like credit card number etc with the server with the confidence that they are interacting with intended site and not the rogue site impersonating the intended site.