i had a beautifull one that went up in a fire--a real heartbreaker that.
i tuned it either traditional portugese tuning--which i forget (this was twelve years ago) or in a open c, which suited several ballards i loved to use it to accompany.
there are easily obtained instruction books from portugal which have english, i found one in vancouver which is not exactly a hot bed of portugese culture.
they are citterns and although the irish didn't traditionally play citterns the scots did. they are very cloase to the late baroque "english guitar" played by the scots.they were played up to about 1870, with a modern revival from stefan sobel and rave richardson, the first one they built and played was based on a portugese guitar.
my lovely old one had brazillian rosewood back and sides and a lovely spruce carved top, at least 100years old, but that's life.
musical instruments make great firewood, i couldn't even find a spot of grease where it ahd been hanging, those resins burn quick, and such pretty colors, although i don't recomend it