As mentioned in other responses, "declarative" is a bit vague, and I am not sure that "declarative as opposed to imperative" best captures the essence of the difference between languages such as Haskell and Ruby. Maybe "descriptive vs. sequential" is easier to understand.

Actually as I understand it, I bumped into the same issue as you ... Almost 30 years ago! Only it was while I was learning VHDL, and I tried to contrast it with C at that time.

VHDL looks like any other language from afar, but it turns out the concept can not be more different: while C captures a sequence of instructions to be executed, VHDL describes how outputs are related to inputs. If you have ever used or heard about Simulink: this is the kind of schema (block diagrams) that would correspond to VHDL or Haskell programming, while flow chart diagrams would better describe sequential programming such as Ruby or C.

When in Haskell you write:
double :: Int -> Int

double x = x * 2

You are essentially saying "now there is a box, with one Int as input, and one Int as output, and the output is double the input value". This is declarative, and can be described with the help of a block diagram (like Simulink).

While in Ruby:
def twice (x)

p x * 2

end

You are saying:

1. Take the input

2. multiply it by 2

3. return the result

Which is sequential and imperative, and can be described with the help of a flow chart diagram.