DIDComm lets people and software use DIDs to communicate securely and privately over many channels: the web, email, mobile push notifications, QR codes, Bluetooth, message queues, sneakernet, and more.
Application-level decentralized protocols are built atop DIDComm. These support activities like secure chat, verifiable credential exchange, buying and selling, scheduling, escrow, bidding, ticketing, and so forth. Search the application-level DIDComm protocol registry to see what you might want to use in your own software:
To implement DIDComm, study the spec or browse the github repo where it's developed: https://github.com/decentralized-identity/didcomm-messaging.
To register or modify a protocol definition, submit a PR against the
/protocols folder of the https://github.com/decentralized-identity/didcomm.org repo.