A digital certificate primarily serves to authenticate the identity of individuals, organizations, or devices within online environments. It is issued by a Certificate Authority (CA) and contains unique information about the entity, including a public key. The certificate ensures secure data transmission by enabling encryption and validating that the sender's identity is trustworthy. Digital certificates are crucial for establishing secure connections across the internet, particularly when using protocols like HTTPS, thereby playing a vital role in online security and the protection of sensitive information.