In the Pacific, the typhoons originate in Micronesia, and regularly hit the Philippines as is the case with Typhoon Megi. In the Atlantic, most hurricanes originate off the west coast of Africa and then veer northward toward the Caribbean, the Gulf of Mexico, southern U.S., the east coast, and ultimately, eastern Canada. An excellent simple graphic of the formation conditions for typhoons or hurricanes can be found here.
If sustained winds reach 74 mph, the storm is officially designated as a hurricane or typhoon. They are typically about 300 miles across, and travel at 15-60 mph until they encounter land, where they rapidly dissipate into "mere" strong rain storms. When Megi made landfall in the Philippines, it was more than 370 miles across. It was the most intense tropical cyclone of 2010 to date.
On the Saffir-Simpson Hurricane scale, Typhoon Megi is a catagory 5, with damage predicted to be "catastrophic". Central pressure in the eye can be <920 mb (compared to >980 mb for smaller category 1 storms, wind speeds >155 mph, and storm surges >18 feet. Hurricane Mitch in October, 1998 left over 9,200 people dead in Honduras, destroyed over 150,000 homes, and caused ~$1 billion in crop damage. Peak sustained winds in Megi have been reported at 180 mph, with gusts estimated to 220 mph. For those interested in aeronautics, these peak winds are Mach number 0.3!!