add a Custom Columns to user

You can use the bellow function for adding custom column to users table:

function modify_user_columns($column_headers) {
    $column_headers['custom_field'] = 'Custom field';
    return $column_headers;
}
add_action('manage_users_columns', 'modify_user_columns');

function custom_admin_css() {
    echo '<style>
    .column-custom_field {width: 8%}
    </style>';
}
add_action('admin_head', 'custom_admin_css');

function user_posts_count_column_content($value, $column_name, $user_id) {
    if ( 'custom_field' == $column_name ) {
        return 'Value';
    }

    return $value;
}
add_action('manage_users_custom_column', 'user_posts_count_column_content', 10, 3);