Doppler is a tool that makes managing secrets for Docker Compose applications easy, allowing developers to securely supply SSL/TLS certificates in PEM format to their applications. To use Doppler with Docker Compose, developers need to install the Doppler CLI and authenticate, then create certificate and key secrets using the Doppler dashboard or CLI. The `docker-compose` file must be configured to mount the TLS certificate and key, and to expand variables correctly for variable expansion inside the container. Once set up, Doppler simplifies the process of managing secrets, including injecting environment variables and certificates into Docker Compose applications. In production environments, Doppler can be used with a Virtual Machine's file system location by scoping a Doppler Service Token to the application code directory, ensuring secure management of secrets across different environments.