If you want to create your own sidebar which is replaceable to any of the default theme sidebars, here is the best way to Create Custom Sidebars. Click on Create a Custom Sidebar
This popup is used to Creating a Custom Sidebar
After filling the requeried fields click on create sidebar.
The id should be unique for each sidebar. If you do not set an id manually, WordPress defaults the name of the sidebars as sidebar-1, sidebar-2, sidebar-3… and so on for all registered dynamic sidebars. Not setting a unique id means that if a plugin or child theme registers additional sidebars, the count gets thrown off, and this can lead to styling problems, among the other things.
The name is the reader friendly identifier for each sidebar—each name displays above its sidebar in the admin view. Most of the time, the sidebar name corresponds to its location in the layout (like Store Sidebar, Upper Sidebar, Footer Area 1, Right Footer Area, etc...).
The description appears in smaller text below the name in the admin view. It tells whoever is working on the site and what the sidebar is intended to do.
Before Title, After Title
These are the opening and closing tags for the title of each widget in your sidebar. WordPress defaults to h2. Ex:- Before Title ='<h3 class="widget-title' After Title ='</h3>'
Before Widget, After Widget
These are the opening and closing tags that contain the widget. These can be whatever element you wish, but a block-level element such as a div or aside is good for clearing elements above and below the widget. WordPress defaults to a li. One thing you should not alter is the id="%1$s" class="widget %2$s" in the before widget argument. This snippet of code is there to make sure that plugins work correctly with your sidebar widgets. Ex:- Before widget = '<div id="%1$s" class="widget %2$s">'
After widget = '</div>'
Here is the Created Custom Sidebar with name of Custom Sidebar