Professor Jane Zatta's background on "The Second Nun's Tale" includes portraits of Saint Cecilia, background information on medieval women's freedom of choice in marriage, and the text of Chaucer's source for the tale.
This page goes into some interpretive issues for both Prologue and Tale. Of note is an interesting section comparing the Prologue to a medieval triptych, a three-paneled altarpiece meant to juxtapose related religious scenes.
Here's a link to the first page of "The Second Nun's Tale" in the Ellesmere Manuscript, along with an illustration of the Second Nun.
An altarpiece dated 1304 from a medieval Italian church. Click on the image to see the scenes from Cecilia's life in more detail.
This page, provided by Harvard, offers ten lessons that start with a general explanation of the principles of Middle English pronunciation and move on to actual practice with the tales themselves.
This is a helpful glossary of Middle English terms often used in Chaucer. The 100 most common words are denoted by an asterisk.