5. Enable My Domain

To use Lightning components, your org needs to have My Domain enabled. Skip this step if it is already enabled.

Go to Setup > Company Settings > My Domain.

Follow the steps in this document to enable My Domain: https://help.salesforce.com/articleView?id=domain_name_setup.htm&type=5. For more information, see https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/intro_reqs_my_domain.htm.