Digital Signature is a Digital Identity of a person/organisation. Using a Digital Signature a person can sign documents , file returns, apply for tenders etc.
Digital Signature is different from hand-written signature or electronic signature. Electronic signature is scan copy of a handwritten signature it has no legal value, whereas a Digital Signature is issued by a Government approved Certifying Authority and has legal binding .
This is most popular class of certificates, and most applications would recognize this class of certificates.
This level of assurance is required generally by Tender portals and some highly sensitive websites.
If you opt for class 3 certificate, all applications which are created for Class 2, should be able to recognize your certificates.
The DSC could only be used for Signing a document. (The most popular Certificate)
The most popular usage is signing the PDF file for Tax Returns, MCA and other websites.
The DSC would be used to Encrypt a document, it is popularly used in tender portal, to help your company encrypt the documents and upload.
You could also use the certificate to encrypt and send classified information.