You have to follow the below configuration steps to add the ‘Quick Metadata Search’ home page component in the sidebar and start using metadata search features.
- Navigate to the Setup

- Customize -> Home -> Home Page Layouts

- Click on the Edit button to edit the homepage layout named DE Default.

- Select the Quick Metadata Search checkbox to enable the Metadata search component on the home page. Click Next.

- Order the components and Click on Save.

- After adding the component on the Home Page, it will appear as follows -

PS: View Metadata Search, Salesforce quick search app on Salesforce AppExchange: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N30000009wgF7EAI