Before you start this lightning component tutorial, you have need to 2 things -:
A Free Salesforce Developer Org. [If you don’t have? Sign up Here]
Enable Custom Domain To Your Org. -:
So what is custom domain and why we need to have it, to learn Lightning Components? So basically, A custom domain or My Domain is a way to have your own Salesforce org customized URL rather than a common Salesforce URL.
For Example :
Your Salesforce Org. default assigned URL looks Like : https://ap4.salesforce.com/home/home.jsp
After Register a Custom My Domain, URL looks Like : https://yourCustomDomain.my.salesforce.com/home/home.jsp
To display lightning components in Lightning tabs, Lightning Pages, the Lightning App Builder, or lightning standalone apps, your organization needs to have a custom domain configured using My Domain.