A typical wireless router is 802.11g, or wireless-G (the 802.11 is the IEEE name for Wi-Fi, the G stands for the protocol). A router that supports 802.11n, or wireless-N, is just faster. All wireless-N capable routers are backward compatible though.
802.11g is 54 megabits/second, or 6.75 megabytes/second. 802.11n is up to 300 megabits/second, or 37.5 megabytes/second. In comparison, a standard CAT5 ethernet cable is only 100 megabits/second or 12.5 megabytes/second.
So basically wireless-N is just a lot faster.
The thing is, wireless-N isn't a finalized standard yet, which is why everything is "Draft N".
Keep in mind though, your wireless adapter must support wireless-N to get the faster speeds.