"Digital editions" can come in a variety of flavors. Comparing different online versions of Samuel Johnson's biography of Milton in the Lives of the English Poets reveals different interests, priorities, and affordances across sites.
Scholarly editions often offer more advanced features than general archives. Comparing what's available in these markedly different sample projects will reveal some of the decision making that should be completed before embarking on a digital edition of one's own.
Working with an advanced technology, like the Text Encoding Initiative, can be daunting. These examples from the Women Writers Project, however, demonstrate that the basic logic of TEI encoding is straightforward and user-friendly. Mastery is a matter of slowly learning the individual pieces of the Guidelines that an editor needs for the demands of a project.
With just a little familiarity with the Guidelines, even fully-functioning TEI projects are legible to the beginner. Try reading parts of the underlying XML code in these online publications. Such "real-world" examples can be very helpful in resolving one's own encoding questions.