The easiest ways to access Taiwan are by plane and by boat.
The major airports of Taiwan are Taoyuan International Airport close to Taipei, Kaohsiung International Airport, Taipei Songshan Airport, Taichung Airport and Hualien Airport. When you are checking in, you will have to show the authorities an onward or return flight ticket. There are airports at Makung, Taitung, Kinmen which have cross-strait flights to China. EVA Air is the leading carrier of Taiwan.
Star Cruises is a line that has services from Keelung and Kaohsiung to Hong Kong. Fujian Province has two daily ferries that go to Matsu. From Matsu, there are two more ferries to Keelung. Mawei harbour gives you the chance to buy an inclusive ticket to Taipei, which includes the ferry ride and a domestic flight from there to Taipei. Ferry services also exist between Xiamen and Quanzhou.