Presumably, before you start using Web-API you need to be able to write your own "request" which describes the data you wish to download

Presumably, before you start using Web API you need to be able to write your own "request" which describes the data you want to retrieve. For that you need :

• to have an idea of what is available from our archive
• to decide what you wish to download
• to know how to write the request. For long requests you should read the Guidelines to write efficient MARS requests.