Having over 600+ tests and so much additional resources, we know that it can be quite overwhelming to go through everything. We would recommend getting started with the ranking factors sheets, most especially the positive ranking factors sheet as these are tests that we've done that we've already sorted and summarized. You could start with the positive ranking factors so you already have available information that you could apply to your sites immediately since we've tested and have verified that they can affect rank.
We also have our one liner reports which is a PDF file that lists down all our tests and a short summary of the result, most often just a one line explanation, thus called one liner report :)
If you are looking for a particular topic, you can also use the search function and it will show you any tests, summary, chats, that mentioned the topic.
In case you need additional assistance, you can also email us at firstname.lastname@example.org