Answer:
Well first and foremost, the most important thing to understand is that the pasta is dried, which may sound funny but it critical. Next, osmosis. Osmosis is a type of diffusion that specifically involves water. Heat makes the reaction occur faster (I believe?).
Having said that (established the definitions), we can move on to explaining why cooking dried pasta in boiling water makes the pasta soft. The idea of diffusion is based on the concept that substances will move from areas where there are more concentrated to areas where they are less concentrated. Because there is way more <em>free water</em> present in the surrounding environment of the dried pasta, the water will diffuse into the pasta, making it moisturized and hence soft. Further, there are more solutes present in the pasta, another reason as to why diffusion will occur.
As to heat, I'm not quite sure as to its effect, but heat does tend to make reactions faster. It may have an effect on making the pasta soft, I guess. As the temperature of the dried pasta is much lower than that of the boiling water when you start to boil the pasta, the heat will move into the pasta, as heat also tends to move from hotter to colder substances, making it (softer?). Hope this helps :)
As to websites, I have to admit I was kinda lazy but it should be easy to find websites on the info above. Some good sources include Sciencing, Khan Academy, etc.
