You can connect to MaQiaTTo Broker with below devices via provided sample code.
To connect via Linux based devices (Raspberry, Beagle Bone, Ubuntu etc.) click here.
To connect using ESP8266 click here.
You can test your configuration by connecting HiveMQ's MQTT over Websocket client like in figure below.
Follow up steps 1 to 4 to connect, subscribe, publish and receive the messages via maqiatto.com.
You can use your Mosquitto MQTT client's console tools called mosquitto_pub/sub.
USe command line tool like denoted below with given parameters.