What are APIs? - APIs are application programming interface! This idea behind them is to send a request to a website or server and wait for a response from that source. The response can then be used for any application or program.
Why are APIs useful? - APIs allow us to get data from sources that are not from our own database or server. For example, lets say that you have a page on Facebook for your Florist business! You can change, adjust or retrieve data from your page with API routes. An example would be getting the data for a certain event that you are hosting at your Florist shop, to get this data, you would use: GET /v6.0/{event-id} to the graph.facebook.com server.
How do I start using APIs? - Good Question!
REST APIs are requests that are sent through HTTP protocols. These are web based APIs so they are making GET and POST calls through urls. The Florist shop example above shows an example of the type of REST call and the extension to add to the end of the Facebook API url. (Side-note: many websites will have separate urls for API routes.)
Example sites to help learn about Python APIs: