A Digital Signature Certificate explicitly associates the identity of an individual/device with a pair of electronic keys - public and private keys - and this association is endorsed by the CA. The certificate contains information about a user's identity (for example, their name, pincode, country, email address, the date the certificate was issued and the name of the Certifying Authority that issued it).
These keys complement each other in that one does not function in the absence of the other. They are used by browsers and servers to encrypt and decrypt information regarding the identity of the certificate user during information exchange processes. The private key is stored on the user's computer hard disk or on an external device such as a token. The user retains control of the private key; it can only be used with the issued password.
The public key is disseminated with the encrypted information. The authentication process fails if either one of these keys in not available or do not match. This means that the encrypted data cannot be decrypted and therefore, is inaccessible to unauthorized parties.