How to implement login and login maintenance on Android when using REST API

Hello.

I am a very beginner in programming.

I've worked on REST api through Django (django-rest-auth), but I have no idea how to implement login here, so I'm posting a question here.

The api I made is json type

{
    "username": "",
    "email": "",
    "password1": "",
    "password2": ""
}

After sending the in a post manner

HTTP 200 OK
  Allow: POST, OPTIONS
  Content-Type: application/json
  Vary: Accept

  {
    "key": "99defb355414133f00ad88e15771e3a8b43e71f"
}

In this way, the key value is received in json type. I don't know why they give me this key.

Does giving this key value mean basic authentication?

    "description": "Check the credentials and return the REST Token\nif the credentials are valid and authenticated.\nCalls Django Auth login method to register User ID\nin Django session framework\n\nAccept the following POST parameters: username, password\nReturn the REST Framework Token Object's key.",

I'm asking because I don't even know what I should study with just this explanation.

I don't know which part to study or how to implement it.

I'd appreciate it if you let me know.

I heard retrofit is good, so I want to apply it here, but I don't know what to do.

I don't know how to log in or maintain it, so I'd appreciate it if you could give me a little hint.