Sometimes, you get this error message. That means you are a user who has no permission to write the site source code. To update this you can use this command in the terminal if you want to writable whole site. You also can specify the themes or plugins which you want to writable.
Widgets are helpful elements of Wordpress. It makes user can simply drag and drop elements into their site. There are many themes uses their custom widgets to make their themes more .flexible and allows users to create their own layouts
Sometimes after you register a custom post type. You return single page and you did not see the comments form there. Although you used comment_form() or comments_template() function in your template file