Singapore is a major transit hub in south east Asia, not only for plane flights but road, rail and sea transport. Most tourists fly in and out of Changi International Airport located at the eastern end of Singapore island. Many are transit passengers who might wait a few hours at this modern Singapore airport. Some fly south to Australia and New Zealand. Some north to China, Vietnam, Korea and Japan while some fly north west to Malaysia, and Thailand etc while others go much further to Europe. Some fly east to the Philippines and America.
By road transport out of Singapore: Because of the great expense of car ownership in Singapore few private cars drive up the Malay peninsula, starting with passing through Jahor Baru, southern sultanate of Malaysia. I shared a taxi in 1976 with 3 Chinese girls going to Ipoh. From there I caught a bus to Bangkok Thailand. The train out of Singapore up the Malay peninsula is not the fastest train in the world yet, but it's comfortable and interesting.