First of all what is swarl - this is abbreviation for Shortwave Amateur Radio Listening. The site is committed to SWL (short wave listening) hobby and this is the hobby of thousands of people around the world. Maybe you payed attention and saw a few large antennas standing on the roof of some houses or on the tall post. Well, this is the first sign of amateur radio hobby. I can secretly tell you what is happening under that huge antenna - there is a guy or lady sitting with his/her little radio transceiver, microphone, headset, and maybe a telegraph key for morse code transmitting. I hope i didnt write too many unfamiliar words for you to spoil your interest. Well, now, when you imagine that picture of the guy with the radio, think on following piece of information: The Amateur radio operator only allowed to have transmitter which transmits with very little power, in very narrow band, and on limited frequencies. With all those conditions radio operators are able to communicate with others like them everywhere around the globe and even with space expeditions. Now exciting part, There is no need of special permissions for listening radio in your own little radio shack, you can be SWL(see above) without any payments, well, except the price of radio of course. Now, the basic point of this hobby is to "catch" that long away standing or rare private radio station and exchange a little post card with it as a confirmation of the work of that station at this particular time. This little card is called QSL and if you make google search for that word you will find thousands of pictures of those cards from really rare stations like Vatican station or North Pole or South pole, or even space station. After all this hobby is very close to the hobby of fishing, and the price of the radio receiver is comparable to the price of fishing equipment.
Hope I explained the basics of the SWL hobby and here is the site that may help you to start with this hobby: http://swarl.org