The word "Philosophy" comes from Greek:
So "Epistem" + "ology" literally means "Words about Knowledge." Epistemology encompasses what Knowledge is, whether and how humans can interact with Knowledge, and systems of organizing knowledge so that humans can make use of it.
Epistemology relates to Metaphysics because Reality (i.e. what truly exists) and what/how one knows about that reality are closely related questions.
Epistemology relates to Logic because Knowledge plays an essential role in Reason.
Positions held or rejected under Epistemology can affect the following sub-fields under Applied Philosophy: