use ::begin(WiFiClient, url)

The ::begin() function is used in C++ to initialize a WiFiClient object and establish a connection to a specified URL. Here is a step-by-step explanation of its usage:

1. WiFiClient is the name of the class that represents a client connection in a WiFi network. It is part of the Arduino library and provides methods for establishing and managing network connections.

2. The :: operator is the scope resolution operator in C++, used to access static members of a class. In this case, it is used to access the begin() function of the WiFiClient class.

3. The begin() function is a member function of the WiFiClient class. It is called to initialize the WiFiClient object and establish a connection to the specified URL.

4. The begin() function takes two parameters: the WiFiClient object that is being initialized, and the URL of the server to connect to. The WiFiClient object is passed as the first parameter using the :: operator to separate the object from the function.

5. The begin() function performs the necessary initialization steps to establish a connection to the specified URL. This includes setting up the network connection, resolving the server's IP address, and establishing the TCP/IP connection.

6. After the begin() function is called, the WiFiClient object is ready to be used for communication with the server. Methods like write(), read(), and available() can be used to send and receive data over the established connection.

It's important to note that the begin() function may return a boolean value indicating whether the connection was successfully established or not. This return value can be used to handle any errors that may occur during the connection process.