Don?t String me Along!

Pun intended. Newbie here with first of a life long series of fly tying questions. Step wise, here?s the deal. Got me a Danvise. Did not want to go wild so bought some Gurgler Kits by Lee Haskin, thinking they had EVERYTHING to tie a fly, which for the most part, they do. However, they DO NOT HAVE thread.

The instructions say I need Red and White 3/0 Uni-Big Fly.

Questions:
What is that?
Where do I get it?
How much should I get?
Should I get other colors at same time?
Should I get different kinds?
This pattern is for 1 to 2/0 size, but they reduced it for me to size 6, is the 3/0 too big for size 6? And if it is too big, what size do I need?

Thank You for your help!