Hi Bennet,
First of all, I would like you to turn to pg 89 of your PMBOK 6, it has a full list of all the project plans and documents
As a general rule of thumb, Project Plans are the HOWs and Project Documents are the WHATs.
For example, if you are not sure whether a certain occurrence should be considered a risk, consult the Risk Management Plan. If you want to know what risks have been identified so far, consult the Risk Register.