retrieve data points from private channel | ThingSpeak API | Forum

OK - I figured it out - no need to pay attention to the post ...
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I'm trying to understand how to use the write API to retrieve data points from a private thingspeak channel.
I have set up a feed for sending data to a channel on one device, but now I want a different device - an Arduino - to read each data point, but I'm kind of confused on how to go about it and have been unable to find any information online.
Would appreciate pointers or examples.

EDIT:
To be more specific, which is always a good start when looking for a helpful answer...
I'm seeking information on the use of the React app and the ThingHTTP app for the Arduino. I'm uploading data to ThingSpeak with one device and want to download/read that data with another device, an Arduino, which will then switch on a relay.
The uploading data part is straightforward and there are loads of examples available online, however, the download of data seems to be a bit more cumbersome and less documented.
I thought it would be possible to use React to trigger a ThingHTTP request in order to fetch each data point in the channel. And I still believe that it is possible, but I'm slightly bamboozled by the explanation on http://community.thingspeak.com/documentation/apps/thinghttp/
Specifically:

Parse String
ThingHTTP sends back the full response that is generated by the request. If you are looking to extract a piece of data from the response, you can add a Parse String to the ThingHTTP Request. This feature allows you to do the parsing on the ThingSpeak side instead of wasting code space on the device / microcontroller side. The format is Parent_cell.child_cell etc. If you also know the full XPATH to the data, you can specify the XPATH as the Parse String.

What does the Parent_cell.child_cell format refer to, how does it translate to normal people speak, and how can I use it to trigger a reaction on my arduino.

Thanks.

Moxi