How do I create a custom lightning component in Salesforce?

Open the Developer Console.
Select Developer Console from the Your Name or the quick access menu (Setup gear icon).
Open the New Lightning Bundle panel for an Aura component.
Select File | New | Lightning Component.
Name the component.
For example, enter helloWorld in the Name field.
Describe the component.
Use the Description field to add details about the component.
Add component configurations to the new component.
You can select as many options in the Component Configuration section as you wish, or select no configuration at all.
Click Submit to create the component.
Or, to cancel creating the component, click the panel’s close box in the top right corner.