One can publish platform events via Apex (Apex is a language used in Salesforce to write business logic) or via SOAP and REST API.

To demonstrate how one can publish an event using platform events, let's run a simple Apex code from the developer console:

    List<Temperature_Sensor__e> temperatureSensorEvents =
        new List<Temperature_Sensor__e>();
    temperatureSensorEvents.add(new Temperature_Sensor__e
      (CustomerId__c='12345', DeviceId__c='12345', Temperature__c=30));
    temperatureSensorEvents.add(new Temperature_Sensor__e
      (CustomerId__c= '12345', DeviceId__c='10013',Temperature__c=40));

    // Call method to publish events
    List<Database.SaveResult> results = EventBus.publish
      (temperatureSensorEvents);

    // Inspect publishing result for each event
    for (Database.SaveResult sr : results) {
      if (sr.isSuccess()) {
        System.debug('Successfully published event.');
      } 
      else {
        for(Database.Error err : sr.getErrors()) {
          System.debug('Error returned: ' +
          err.getStatusCode() +
          ' - ' +
          err.getMessage());
        }
      } 
    }

Open the developer console using the Setup menu and run the preceding code:

Using the Salesforce REST API or SOAP API, a device can push these events to Salesforce. For our examples, the API to publish the events will be as shown in the following code. A third-party client needs to make an HTTP POST to the following URL:

/services/data/v40.0/sobjects/Temperature_Sensor__e/

The sample payload any device needs to be pushed as shown here:

    {
      "CustomerId__c": "12345",
      "DeviceId__c": "12345",
      "Temperature__c": 50 
    }