HTTP is a request-response protocol. The client sends a request (method, path, headers, body). The server returns a response (status code, headers, body).
Common methods: GET (read), POST (create), PUT (replace), PATCH (update), DELETE (remove). Status codes: success, redirect, client error, server error.
HTTPS adds TLS encryption. The client and server perform a handshake to establish a secure channel. All data is encrypted in transit. You should always assume HTTPS in system design.