> how [microservices] comunicate between different apps/languages ? they use rest api or is better use something like zeromq/rabbitmq ?

Everything you mentioned, and then several other mechanisms. Whatever happens to be fashionable where they are being implemented.

> Sorry to post this here, but honestly I often hear about microservices but I don't really understand what they are.

A bunch of small applications running separately that talk to each other using different protocols (sometimes one of the RPC protocols, sometimes raw HTTP that is today called REST, sometimes ZeroMQ or AMQP or some other ESB). The idea has little more in it than this, though operationally there are still some things to figure out.