As a wannabe computer "scientist" I have problems differentiating theory and practice Specifically I'm studying towards a research degree in HCI (human computer interaction). I have problems however differentiating theory and practice, or science and engineering. I know science is about advancing human knowledge. Providing evidence about something specific in a field. But it's also about theory right? I guess there's different ways to do science; you can prove something with numbers and results, but you can also do science simply by creating a new method or theory about how something should work right? Engineering on the other hand is more about putting into practice the theory, right?

I'd like to have some guidance, perhaps with examples, to what differentiates theory and practice, science and engineering. Also books/articles to read on the subject would be greatly appreciated.

PS: In HCI it's hard to do research with experiments - it's very subject and not quantifiable as other fields of computer science. Perhaps this is why my confusion is greater than one would expect.
There is no universal objective answer to the question of how to tell what counts as theory and what counts as practice, or what counts as science vs engineering; the precise dividing line between theory and practice, or science and engineering, is subjective and a matter of opinion.  Those terms are not precisely defined -- they are fuzzy, subjective terms.  Different people use them differently.

For instance, sometimes people might use science to mean "understanding fundamental questions, identifying and testing laws of nature and hypotheses" and engineering to mean "building useful systems and solving practical problems", but even there the line is fuzzy.  Other times people use the term "science" to mean "what I do" or "the kind of work I respect" or "the really challenging stuff" and "engineering" to mean "what those other researchers do" or "the kind of work that I consider trivial/uninteresting/not deep".  You'll probably encounter many other variations on these kinds of meanings.

P.S. You are wrong that it's hard to do research with experiments in HCI.  Indeed, every human subjects study is itself an experiment, so experiments are very commonly used in HCI.  Perhaps you are thinking that it is challenging to find universal laws of nature in HCI (analogous to Newton's First Law, say, but for people), as people are complex.  That is true, but it doesn't mean no such laws exist or that such research is impossible.  Consider Fitt's Law, for instance.