In this video Dan Vanevenhoven N9LVS gives you the basics of Radio Propagation: including Sun Spots, Solar flux, K and A factors.
Why should you be interested in propagation? Well if you want to make those DX contacts you will need to be aware of when propagation is best for conditions to your target. One way to do this is to listen. Another is to check propagation sources such as WWV mentioned above. You can also get familiar with the propagation tables presented monthly in QST and CQ magazines. These charts will tell you when to expect the best propagation on what bands and at what time for your location to other areas of the world. An excellent source is to check the DX clusters online or by packet radio. This can give you current information about DX activity that is happening right now.