Hi @LuisPereira ,
Great that you are interested in MQTT and HiveMQ, welcome to the community!
broker.hivemq.com is a test broker, all data on it is public and visible to anybody, it is not using any SSL (TLS) and thus is easy to connect and run a test.
For getting started with HiveMQ Cloud please start by checking Frequently Asked Questions. You can download server CA from here. Note that in order to stable a connection to the HiveMQ Cloud cluster, your MQTT client must support and use SSL-SNI extension (server name indication).
I hope this helps
Regards,
Dasha from HiveMQ team