stm32 tcp_echoclient example

Can you please explain the following steps in detail in the the tcp_echoclient example.

       /* pass newly allocated es structure as argument to tpcb */

       tcp_arg(tpcb, es);

       /* initialize LwIP tcp_recv callback function */

       tcp_recv(tpcb, tcp_echoclient_recv);

       /* initialize LwIP tcp_sent callback function */

       tcp_sent(tpcb, tcp_echoclient_sent);

       /* initialize LwIP tcp_poll callback function */

       tcp_poll(tpcb, tcp_echoclient_poll, 1);

       /* send data */

       tcp_echoclient_send(tpcb,es);