does "that" mean "so"?

Can anybody explain if i can use "that" instead of "so"?
if we can use, can you explain the resource grammar book expressing it?
Can you explain the issue on the following questions?

1.question
Diet Pills Don't Actually Work That Well. [ Does "that" mean "so"?]

2. question.
I didn't know the area THAT well.But the navigation system's simple
directions made getting around a lot easier.

[What does "THAT" mean ?]

.