Question About Understanding Meanings of Binance C++ API Websocket Code

Friends, I am trying to learn Binance C++ API for algorithmic trading on Binance platform. Here is the github page for Binance C++ API: https://github.com/tensaix2j/binacpp I am copying a code example from above github project and have a few questions. I pretty much understand everything in the code example but do not understand the last three lines of the code and their precise purpose. Here are the three lines I what to understand.

BinaCPP_websocket::init();
BinaCPP_websocket::connect_endpoint( ws_depth_onData ,"/ws/bnbbtc@depth" );
BinaCPP_websocket::enter_event_loop();

Can somebody explain the meanings and significance of each of the three lines of code above. Do I have to place these lines at the end of the code or I could possibly place them at start of the code.

Here is the full code example from github project on Binance C++ API.

    #include <map>
    #include <vector>
    #include <string>


    #include "binacpp.h"
    #include "binacpp_websocket.h"
    #include <json/json.h>



    using namespace std;

    map < string, map <double,double> >  depthCache;
    int lastUpdateId;

    //------------------------------
    void print_depthCache() {

    map < string, map <double,double> >::iterator it_i;

    for ( it_i = depthCache.begin() ; it_i != depthCache.end() ; it_i++ ) {
        
         string bid_or_ask = (*it_i).first ;
         cout << bid_or_ask << endl ;
         cout << "Price             Qty" << endl ;      

         map <double,double>::reverse_iterator it_j;

         for ( it_j = depthCache[bid_or_ask].rbegin() ; it_j != depthCache[bid_or_ask].rend() 
         ; it_j++ ) {

         double price = (*it_j).first;
         double qty   = (*it_j).second;
         printf("%.08f          %.08f\n", price, qty );
         }
       }
    }





    //-------------
    int ws_depth_onData( Json::Value &json_result ) {

        int i;

        int new_updateId  = json_result["u"].asInt();

        if ( new_updateId > lastUpdateId ) {

        for ( i = 0 ; i < json_result["b"].size() ; i++ ) {
            double price = atof( json_result["b"][i][0].asString().c_str());
            double qty  = atof( json_result["b"][i][1].asString().c_str());
            if ( qty == 0.0 ) {
                depthCache["bids"].erase(price);
            } else {
                depthCache["bids"][price] = qty;
               }
        }
        for ( i = 0 ; i < json_result["a"].size() ; i++ ) {
            double price = atof( json_result["a"][i][0].asString().c_str());
            double qty  = atof( json_result["a"][i][1].asString().c_str());
            if ( qty == 0.0 ) {
            depthCache["asks"].erase(price);
            } else {
                depthCache["asks"][price] = qty;
            }
        }       
        lastUpdateId = new_updateId;
   }
   print_depthCache();
}


    //---------------------------
    /*
    To compile, type
    make example_depthCache

    */

   //--------------------------

    int main() {

        Json::Value result;
        long recvWindow = 10000;    

    
        // Market Depth 
       int i;
       string symbol = "BNBBTC";
       BinaCPP::get_depth( symbol.c_str(), 20, result ) ;

       // Initialize the lastUpdateId
       lastUpdateId = result["lastUpdateId"].asInt();
    
       for ( int i = 0 ; i < result["asks"].size(); i++ ) {

            double price = atof( result["asks"][i][0].asString().c_str() );
            double qty   = atof( result["asks"][i][1].asString().c_str() );
            depthCache["asks"][price] = qty;
       }
       for  ( int i = 0 ; i < result["bids"].size() ; i++ ) {

           double price = atof( result["bids"][i][0].asString().c_str() );
           double qty   = atof( result["bids"][i][1].asString().c_str() );
           depthCache["bids"][price] = qty;
      }
      print_depthCache();


      BinaCPP_websocket::init();
      BinaCPP_websocket::connect_endpoint( ws_depth_onData ,"/ws/bnbbtc@depth" ); 
      BinaCPP_websocket::enter_event_loop(); 

    }