For many people their only introduction to radio telescopes came from the movie Contact which featured the Arecibo radio telescope (which also featured in GoldenEye) and the Very Large Array (VLA). While the radio telescopes have been used to search for extraterrestrial life, their main purpose is to look into parts of the galaxy, and other galaxies, that other telescopes cannot see.
The reason why these telescopes are so important is because they have the ability to see some of the coldest, densest gas in a galaxy. By dense I mean 100-10,000 particles per cubic centimeter (yes that's particles/cm^3). For comparison air at sea level has about 10^19 particles/cm^3 (that's 10,000,000,000,000,000,000) and water has about 10^22 particles/cm^3. So dense is a relative term, but compared to the average density of gas in the galaxy (~1 particle/cm^3), it is pretty dense.
So why are these regions so important? Basically this is where stars, and planets form. It is these dense regions where we find the newest stars, and possibly get a glimpse of the planets forming around them. This will help us learn how solar systems form and will help guide us in our search or life bearing planets beyond our own. In short, it teaches about how we got here, and where our nearest neighbors might be.