add_action('init', 'process_post_data');

function process_post_data() {
    if( isset( $_POST ) ) {
        // process $_POST data here
    }
}

add_action('init', 'process_get_data');

function process_get_data() {
    if( isset( $_GET ) ) {
        // process $_GET data here
    }
}

add_action( 'init', function() {
    register_post_type( 'event', array(
            'public' => true,
            'label'  => 'Events'
        );
    );
});

Registers a new custom post type with a label Events and a slug event