The default sidebar on WordPress blogs consists of five separate Widgets. Widgets are objects with pre-defined functionality that can be customized.

Default WordPress sidebar

Five widgets comprise the default sidebar
To customize your Sidebar, click the Widgets link in the Dashboard’s Appearance menu.

Appearance > Widgets
WordPress offers about 20 ready-made widgets. You can add widgets to your sidebar, as well as remove, arrange and customize them, from the Widgets page.

Manage sidebar widgets from the Widgets page
The right column of the Widgets page represents your main sidebar. Each button in the Main Sidebar panel represents a widget.

Sidebar widgets
Click the inverted triangle on a button to reveal widget properties you can customize.

Click triangle to reveal Widget settings
To add a new widget to your sidebar, drag it from the Available Widgets area and drop it onto your sidebar. Notice how widgets already in your sidebar move aside to make room for the one you’re adding.
Rearrange the widgets in your sidebar by dragging & dropping.
To remove a widget, drag it off your sidebar and drop it into the Available Widgets area. If you want to remove a widget, but preserve customizations you have made for later use, drop it into the Inactive Widgets area at the bottom of the Widgets page.