The G3 API functions can be classified in multiple dimensions:
GET/POST / streaming POST (document is passed as a stream) / batch POST (multiple documents analysed in a single request)
specification of the document:
plain text with an optional title / a sequence of paragraphs / non-plain text (html, pdf, …)
analyses (the values can be combined):
See this page for quick start instructions. See swagger Swagger documentation for more technical info.