How to save Meta Data in WordPress back-end with PHP

I am relatively new to Post Meta Data in the WordPress backend using PHP. I have written the code that creates the Meta Data. I need help saving the data for which I have written. It will also need to allow me to edit the data once saved.

In this case its for a text field.

I have created the Meta Data for the input field which displays well in the back-end WordPress admin area.

add_action( 'add_meta_boxes', 'cd_meta_box_add' );
function cd_meta_box_add()
{
    add_meta_box( 'my-meta-box-id', 'Job Title', 'cd_meta_box_cb', 'people', 'normal', 'high' );
    /* Save post meta on the 'save_post' hook. */
    add_action( 'save_post', 'cd_meta_box_add', 10, 2 );
}

function cd_meta_box_cb()  
{  
    echo "<input type='text' name='jobtitle'>";     
} 

I just need assistance with the code that will save the above Meta Data to the DB and allow for editing and revisions

You were almost there.

The final part of the puzzle is the function that saves the metadata, but first we need to make a few adjustments to your existing code:

1. add_action( 'save_post', 'cd_meta_box_add', 10, 2 ); has to be moved outside cd_meta_box_add(), and

2. Change add_action( 'save_post', 'cd_meta_box_add', 10, 2 ); into add_action( 'save_post', 'cd_meta_box_add' ); as this action hook only receives one parameter (the post ID), and

3. You need to define the function that will process the data (and it can't be cd_meta_box_add as you have it now so we'll create a new one called save_cd_meta_box_data).

/* Save post meta on the 'save_post' hook. */
add_action( 'save_post', 'save_cd_meta_box_data' );

function save_cd_meta_box_data( $post_id ) {

    // Autosaving, bail.
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
        return;
    }

    // @TODO
    // You should add some additional security checks here
    // eg. nonce, user capabilities, etc, to prevent
    // malicious users from doing bad stuff.

    /* OK, it's safe for us to save the data now. */

    // Make sure that it is set.
    if ( ! isset( $_POST['jobtitle'] ) ) {
        return;
    }

    // Sanitize user input.
    $my_data = sanitize_text_field( $_POST['jobtitle'] );

    // Update the meta field in the database.
    update_post_meta( $post_id, '_job_title', $my_data );
}

4. Now that we're successfully saving the metadata into the database, let's allow the user to view it / edit it:

function cd_meta_box_cb( $post )  
{  
    $job_title = get_post_meta( $post->ID, '_job_title', true );
    echo "<input type='text' name='jobtitle' value='" . esc_attr( $job_title ) . "'>";     
}

---

The final code should look like this:

/* Register and display metabox */
add_action( 'add_meta_boxes', 'cd_meta_box_add' );

function cd_meta_box_add()
{
    add_meta_box( 'my-meta-box-id', 'Job Title', 'cd_meta_box_cb', 'people', 'normal', 'high' );
}

function cd_meta_box_cb( $post )  
{  
    $job_title = get_post_meta( $post->ID, '_job_title', true );
    echo "<input type='text' name='jobtitle' value='" . esc_attr( $job_title ) . "'>";     
}

/* Save post meta on the 'save_post' hook. */
add_action( 'save_post', 'save_cd_meta_box_data' );

function save_cd_meta_box_data( $post_id ) {

    // Autosaving, bail.
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
        return;
    }

    // @TODO
    // You should add some additional security checks here
    // eg. nonce, user capabilities, etc, to prevent
    // malicious users from doing bad stuff.

    /* OK, it's safe for us to save the data now. */

    // Make sure that it is set.
    if ( ! isset( $_POST['jobtitle'] ) ) {
        return;
    }

    // Sanitize user input.
    $my_data = sanitize_text_field( $_POST['jobtitle'] );

    // Update the meta field in the database.
    update_post_meta( $post_id, '_job_title', $my_data );
}