For downloading the data via web-api, is described here:
https://confluence.ecmwf.int/display/WEBAPI/Web-API+Downloads
Specifically, follow the steps here to install the latest version:
https://pypi.org/project/ecmwf-api-client/
Briefly, install with the pip command:
(I actually needed this on the ECMWF system pip install --user ecmwf-api-client)
Login and retrieve your "key":
Login:
Retrieve your key at:
Create and paste the "key" information in here:
You will also need to accept the terms before you can access the data with web-api.
Accept terms and conditions.