You could read every book ever written about the TT but there is nothing like the experience of actually being present at this unique event.
There are dozens, written by riders and journalists and they get their own angle across very well but from their experiences.
Personally, after 64 years, my advice is to get yourself booked on the ferry, pick a homestay and take a credit card and a debit card. Be ready to go without sleep and eat and drink everything on the menu (kippers and scallops as well )
Just talk to people when you get on the ferry, you will soon make many pals who are spectators like you, and by the time you have seen the full two weeks of the TT period you can write a book yourself.
I have 64 years of happy vivid memories, but to me every year is better than the previous one and I have pals all over the world thanks to the TT.
What do you need to know ?? There are so many books both fact and fiction...Look on e-bay and see if you can get a GS Davison book called TT or Nick Harriss huge full book, again about the history of the TT.
They were wriiten a few years ago but before computers these were our main source of info, the course in pictures, the results of races from 1907 and vivid stories of man and machine............................failing that, there is wikipedia !
There is always my websites to fall back on
http://www.bbhmg.eu and
http://www.ttfan.co.uk
Hope to see you on the Island, I'll take you for a good informative lap in the car !