1. Signup for the Google Custom Search service at https://cse.google.com/cse/ . It's free. When you set up the custom search feature, fill in your podbean site URL, such as http://slug.podbean.com, as the site to search.
2. Get the embed code from google custom search.
3. From your Podcast Dashboard, go to Layout->Sidebar Widgets to add a "Text" widget on your sidebar. Edit the widget by pasting in the google search embed code. Click "Save Changes" on the Sidebar widgets page.