[subject] + 不太 + [adjective]
[subject] + 不太 + [verb] + ([object])
不太 before an adjective means "not very". 不 is read bú here, because 太 is fourth tone.
不好吃 is a flat verdict: the food is bad. 不太好吃 says the same thing gently, and it's what people say to be polite.
不太 also goes before verbs of liking, knowing and being able: 喜欢, 明白, 会, 习惯, 想.
Swapping the two words changes the meaning. 太不 is "far too un-": strong criticism.
不太 takes the place of 很. The two don't stack.