Transport in South East Asia is very easy to use, whether its long distance or just local. Most people speak at least some English and the region is extremely used to tourists so has created an extensive network for travellers.
If you are tight on time it can sometimes be an idea to use domestic or other short distance flights between destinations, as overland travel in South East Asia, while cheap, can be time consuming. There are many discount carriers to choose from, and the key cities double as the key transport hubs. The national airlines are usually pretty good but beware of the really low-cost carriers as these can sometimes have dubious safety records.
One of the most enjoyable ways to travel through South East Asia is by train. Some countries are still without rail networks – most notably Cambodia and almost all of Laos – but most have pretty good routes in place.
Vietnam has a rail route which runs from Saigon in the south to Hanoi in the north, and the Thai capital Bangkok is connected to Chiang Mai in the north, Vientiane, the capital of Laos, and all the way to Singapore via Malaysia due south.
Buses are one of the most fail-safe means of transport in South East Asia: the combined network of tourist and local buses will get you pretty much between any two points you care to mark on a map. Most backpackers opt for the tourist buses, so called because they are slightly more expensive and comfortable than the local versions. Buses are often used for overnight travel, which created a double win: a long distance is covered and you simultaneously save on a night’s accommodation.
You’ll almost certainly hop on a boat at some point while travelling in South East Asia. This means of transport is the only way to reach the various outlying islands, which are hugely popular destinations to varying degrees. If travelling the Indochina loop overland, you’ll probably take a boat between Thailand and Laos, which is one of the classic journeys in South East Asia.