" BTW " stands for " British Traditional Wicca ". This term is used to discuss the original Traditions of Wicca that were first introduced to us back in 1954. These Traditions are said to be descended from the New Forest Coven of which Gerald Gardner was a member in the 1930's and 1940's.
For those with an interest in Traditional Wicca here are some books that I would suggest to better your understanding of it. Granted since the information about Traditional Wicca is oathbound you won't find all the answers in these books. But they will certainly give you a glimpse of what British Traditional Wicca is all about.
"Witchcraft Today" by Gerald Gardner
"The Meaning of Witchcraft" by Gerald Gardner
"High Magick's Aid" by Gerald Gardner (fiction)
"The Witch's Bible Complete" by Janet and Stewart Farrar (Contains the books "What Witches Do" and "Eight Sabbats for Witches"
"Lid off the Cauldron" by Patricia Crowther
"High Priestess" by Patricia Crowther
"Witch Blood" by Patricia Crowther
"The Training and Work of an Initiate" by Dion Fortune
"Wiccan Roots" by Philip Heselton
"Gerald Gardner and the Cauldron of Inspiration" by Philip Heselton
"Triumph of the Moon" by Ronald Hutton
"The Goat Foot God" by Dion Fortune (fiction)
"Lammas Night" by Katherine Kurtz (fiction)
"The Rebirth of Witchcraft" by Doreen Valiente
"Wicca: The Old Religion in the New Millenium" by Vivianne Crowley
"50 Years of Wicca" by Fred Lamond
"Religion Without Beliefs" by Fred Lamond
Here's some good websites to check out for those who are interested in learning more about Traditional Wicca:
The Wiccan Church of Canada: http://wcc.on.ca/
Hope you find these helpful . But remember that the actual teachings of the British Traditional Wiccas is oath-bound and only revealed after one is initiated. Much of the teachings is oral and never written down as well. That being said, you can glean some feeling for the Traditions by reading the books and websites I've mentioned.