I am fairly proficient in Python and have started exploring the requests library to formulate simple HTTP requests. I have also taken a look at Sessions objects that allow me to login to a website and -using the session key- continue to interact with the website through my account.
Here comes my problem: I am trying to build a simple API in Python to perform certain actions that I would be able to do via the website. However, I do not know how certain HTTP requests need to look like in order to implement them via the requests library.
In general, when I know how to perform a task via the website, how can I identify:

the type of HTTP request (GET or POST will suffice in my case)
the URL, i.e where the resource is located on the server
the body parameters that I need to specify for the request to be successful
This has nothing to do with python, but you can use a network proxy to examine your requests.

Download a network proxy like Burpsuite
Setup your browser to route all traffic through Burpsuite (default is localhost:8080)
Deactivate packet interception (in the Proxy tab)
Browse to your target website normally
Examine the request history in Burpsuite. You will find every information you need
Identifying parameters in HTTP request