Using Java to type into my website textbox without a GUI

I want my program to create accounts on my website. Here is what I have so far. What will I need to learn or research to finish this project?

public static String email, password;
    public static void main(String [] args){

    JOptionPane.showMessageDialog(null, "You can only use a GMAIL account.");
    email = JOptionPane.showInputDialog(null, "Enter your gmail account.");
    password = JOptionPane.showInputDialog(null, "Enter your password for every account.");

    beginCreation();