[amandainjames]

I think you want to add a custom widget in your theme. You can add custom widget adding this code in functions.php

function wpblog_widget()
{
    register_sidebar(array(
        'name' => __('Primary Sidebar', 'wpb'),
        'id' => 'primary_sidebar', // unique-sidebar-id
        'description' => '',
        'class' => '',
        'before_widget' => '<li id="%1$s" class="widget %2$s">',
        'after_widget' => '</li>',
        'before_title' => '<h2 class="widgettitle">',
        'after_title' => '</h2>',
    ));

}

add_action('widgets_init', 'wpblog_widget');

Reference: WordPress Custom Widgets

[amandainjames]

I will suggest you to go through a WordPress custom taxonomy tutorial. Here are three steps to create a custom taxonomies in WordPress. To create a custom taxonomy you have to add this code in functions.php

add_action( 'init', 'create_cw_hierarchical_taxonomy', 0 );
//create a custom taxonomy name
function create_cw_hierarchical_taxonomy() {
$labels = array(
'name' => _x( 'Topics', 'taxonomy general name' ),
'singular_name' => _x( 'Topic', 'taxonomy singular name' ),
'search_items' => __( 'Search Topics' ),
'all_items' => __( 'All Topics' ),
'parent_item' => __( 'Parent Topic' ),
'parent_item_colon' => __( 'Parent Topic:' ),
'edit_item' => __( 'Edit Topic' ),
'update_item' => __( 'Update Topic' ),
'add_new_item' => __( 'Add New Topic' ),
'new_item_name' => __( 'New Topic Name' ),
'menu_name' => __( 'Topics' ),
);
// taxonomy register
register_taxonomy('topics',array('post'), array(
'hierarchical' => true,
'labels' => $labels,
'show_ui' => true,
'show_admin_column' => true,
'query_var' => true,
'rewrite' => array( 'slug' => 'topic' ),
));
}