Publishing:

1. Process Builder

2. Flows

3. Apex

4. API ( REST/SOAP)

Subscribing: 

1. Process Builder

2. Flows

3. Apex Trigger

4. CometD

Subscribing to Platform Events using Apex

Check this example – 

Platform Events in Salesforce

Publishing Platform Event using Process Builder

Subscribing to Platform Events from Process Builder in Salesforce