Great question, reader! Segment is our event management/tracking platform. It is not the 'Destination' of where we store our events but it is our event tracking pipeline. The 'Source' of events are coming from our applications. You can get more about what Segment is here.
This doc will go over some implementation details to help with adding Segment tracking to new apps and/or existing apps. The code examples will be for Javascript only (more specifically in Vue) but you can see other language implementations here. Here are some code examples: