How does nrf24l0 work with Arduino Nano and GSM module?

Question

Arduino

There are two Arduino Uno and Arduino Nano boards, they communicate with each other via the NRF24L0 radio module, and then the information is transmitted via the GSM module via sms. So this is how this data transfer happens? I don’t understand the algorithm of work, for example, how do they understand that now you need to turn on and transfer data?