for i=0,1,7 do script.Parent.BackgroundTransparency=i wait() end
How would the 7 change it? I'm thinking it's the time it takes to go from 0 to 1 transparency, but I'm not sure and I don't know how to test it because I haven't noticed a difference.
The 7 in your example would skip numbers. For example, if you have:
for i = 1,10,2 do
That would make the loop go by 2's, making i 1, then 3, then 5, and so on.