You can display a newsletter subscription form in your blog’s sidebar, footer, or any widget area that your theme supports.
To do this:-
Open your WordPress admin dashboard then click on Appearance > Widgets to open the widgets settings page.
Next, select the appropriate widget area then add the “Noptin Newsletter Form” widget.
Finally, select the sign-up form that you want to add then save your changes.
You can use one of two methods to hide or show the widget on specific posts, pages, and post types.