Version 1 of the API uses a RESTful design, accessible only via SSL (https://) to increase security.
All requests to the API require the client to authenticate by using Basic HTTP authentication, so you will need a username and password in order to access any part of the API, this can be obtained by registering for an account on the Portal.
Once you have an account, you can create your API Key (password) from the "Profile' menu link, in the "Security" section of the Portal. The API username is the same username you used to login to the Portal via your web browser.
Full details of how to use the API, along with examples, can be found once you login to the Portal, under the "API" menu link.