The library is very easy to use, first make sure you have all the required jars in the classpath then have a look at the sample source bellow.

public void printContacts() {
    // Setup session and contact manager
    String username = "<gmail username or email address>";
    String password = "<gmail password>";
    GMSession session = new GMSession(username, password);
    GMContactManager manager = new GMContactManager(session);
    // Retrieve all contacts and do some processing on each contact
    GMContact[] contacts = manager.getAllGMContacts();
    for (int i = 0; i < contacts.length; i++) {
        // Do some fancy stuff here

    // Add a new contact
    GMContact contact = new GMContact(
            "TEST TESTINGSSON", 
            "Test comment");        
    contact = manager.addGMContact(contact);

    // Update contact
    contact.setNote("A new note.");
    // Remove contact.
    // End session.
    manager = null;
    session = null;