HTML is not my strong point, but this code section is what prints the messages to the screen
client.println("HTTP/1.1 200 OK");
client.println("Content-type:text/html");
client.println();
// the content of the HTTP response follows the header:
client.print("<p style=\"font-size:7vw;\">Click <a href=\"/H\">here</a> turn the LED on<br></p>");
client.print("<p style=\"font-size:7vw;\">Click <a href=\"/L\">here</a> turn the LED off<br></p>");
// The HTTP response ends with another blank line:
client.println();
Basically it creates the HTML code required by "printing" to the webserver, ie the client
Try this crude example in place of the code above
client.println("HTTP/1.1 200 OK");
client.println("Content-type:text/html");
client.println();
// the content of the HTTP response follows the header:
client.print("<p style=\"font-size:7vw;\">Click <a href=\"/H\">here</a> turn the LED on<br></p>");
client.print("<p style=\"font-size:7vw;\">Click <a href=\"/L\">here</a> turn the LED off<br></p>");
// The HTTP response ends with another blank line:
client.println();
client.println("HTTP/1.1 200 OK");
client.println("Content-type:text/html");
client.println();
// the content of the HTTP response follows the header:
client.println("Hello World");
// client.print("<p style=\"font-size:7vw;\">Click <a href=\"/H\">here</a> turn the LED on<br></p>");
// client.print("<p style=\"font-size:7vw;\">Click <a href=\"/L\">here</a> turn the LED off<br></p>");
// The HTTP response ends with another blank line:
client.println();
Then go and read up on HTML to do it properly !