For the API Reference (and I imagine you are talking about the .eCdoc files), you can simply press 'F1' in the IDE or select Help / API Reference in the menus. Alternatively you can launch 'documentor'.
Unfortunately, as you will soon find out the API docs are still missing a lot of contents and even the contents that is there has not been reviewed.
One big improvement that the upcoming release brings is the transition from those binary .eCdoc files (they are acually 'ear' archives) to ECON
text format. This will facilitate tracking documentation changes through Git and should really help finally sitting down and improving the documentation.
Although it is already very valuable as a quick & up-to-date API listing (Classes, Methods, Properties, parameters, etc...), one of the best source of information at this point remains the samples
, and the community (don't hesitate to ask for help here or on IRC, and do ping me if something goes unanswered for more than 24 hours).