A root certificate [1] is the part of a digital certificate which is responsible for performing authentication processes. The data contained in the root is normally encrypted to prevent other people making changes to the certificate. When you connect to a service or resource which requires this certificate, it uses the data to verify the certificate is authentic and is a correct match.
You may wonder how the encrypted date contained in a root certificate is created. In order to create this data a special type of system, called a certificate authority, is used. During the creation process, two types of digital certificates are created. One certificate is held privately, while the other is shared publically. Both have encrypted data, which must match up, in order to pass authentication processes. While the result will be the same, the computations and methods for arriving at the result can, and do, vary from both types of certificates.
Links:
[1] http://www.digi-sign.com/