Ways to Publish/Subscribe Platform Events in Salesforce?

Publishing:

1. Process Builder

2. Flows

3. Apex

4. API ( REST/SOAP)

Subscribing: 

1. Process Builder

2. Flows

3. Apex Trigger

4. CometD

Publishing Platform Events using Apex

Check this example - http://www.infallibletechie.com/2017/06/platform-events-in-salesforce.html

Publishing Platform Event using Process Builder

Subscribing to Platform Events from Process Builder in Salesforce