Widgets are small blocks of content, which you can find in theme footer or sidebar. They were originally designed to provide a simple and easy-to-use way of giving design and structure control of the WordPress Theme to the user, which is now available on WordPress Themes to include the header, footer, and elsewhere in the WordPress design and structure.
You can access widget edit screen under Appearance > Widgets panel or via Customize on path Appearance > Customise > Widgets. It has three main areas:
To add a widget to your site, drag and drop the name of the widget you want to use from the Available Widgets section into one of the widget areas on the right-hand side of the window. After you have added it, the widget will open up (or if it doesn’t, you can click on the triangle to open it) and you can change the settings and save the widget. The specific settings needed will depend on what type of widget you are using. For instance, if it is a text widget, you just need to type in the text (and optionally, HTML code), and save the widget.