Shortcodes in Sidebar Widgets plugin allows shortcodes to properly execute when they are used in sidebar text widgets.
You can install Shortcodes in Sidebar Widgets directly from the WordPress admin panel. Visit the Plugins > Add New page and search for 'Shortcodes in Sidebar Widgets'. Click to automatically install. Once installed, activate the plugin and it is functional.
The old school install for Shortcodes in Sidebar Widgets plugin:
Download and unzip the file
Upload the full extracted folder to your plugins directory
Activate the plugin through the 'Plugins' menu in WordPress.
You are now ready to use the Plugin according to the directions in the description.