The train system in Singapore consist of two types of trains: Mass Rapid Transit (MRT) trains and Light Rail Transit (LRT) trains. The MRT plies all the major areas, with more lines being constructed currently, while the LRT plies the larger residential areas like Choa Chu Kang and Sengkang.
There are four main lines in the Mass Rapid Transit system: The red North-South Line, the green East-West Line, newly opened orange Circle Line and the purple North-East Line.
(Click to enlarge the MRT Network Map as of Feb 2012, Extracted from SMRT)
The North-South line runs a horseshoe-like shape from Jurong to Marina Bay, taking tourists from attractions like the Singapore Zoo to Orchard Road. A trip from Jurong East to Marina Bay would cost about S$1.90 if you purchased a Standard ticket, and S$1.45 if you bought a CEPAS (Contactless ePurse Application) card (or known more colloquially as 'Ez-Link card').
The green line, or the East-West Line, travels from the Changi Airport or Pasir Ris all the way to Joo Koon, near the Singapore Discovery Centre, passing by the historical district of City Hall as well as the shopping district of Bugis. A ride from end to end would cost S$2.10 for a standard ticket and S$1.94 with an Ez-Link card.
The purple line, or the North-East Line, plys the route from Harbourfront station, from which you can get to Sentosa or Mount Faber to Punggol station. Interesting stops on this line include the Chinese and Indian ethnic area at Chinatown or Little India respectively. Fares would cost up to S$2.10 on a standard card and S$1.86 on an Ez-Link card.
Recently, the government has come up with the Circle Line (or the orange line), which runs from Harbourfront station to Marina Bay, where the majority of the attractions in Singapore lie. Currently in 2012, the line runs from Dhoby Ghaut, where Fort Canning Park and the Istana are, till Harbourfront Station, where Sentosa is located. Other attractions that lie on this line are the Esplanade Theatres on the Bay and the major museums like National Museum of Singapore and Singapore Art Museum at Bras Basah station as well as the Singapore Flyer and Helix Bridge at the Promenade station. The opening of 12 new stations on the Circle Line on 8 October 2011 will also link Singaporeans and visitors by rail to a variety of destinations for work and play, ranging from the popular F&B and nightspot hangout Holland Village, to the lush greenery of Botanic Gardens, to the academic and business hubs of Kent Ridge and one-north. Visitors to Marina Bay Sands can also gain direct access to the mall via Bayfront station, an extension on the Circle line between Promenade and Marina Bay. A one-way trip from Harbourfront to Marina Bay would cost about S$1.40 with a standard card and S$1.15 with the Ez-Link card.
If you want to get a standard card, just get to the MRT train station and head to the ticketing machines where you select your destination and get a standard card for that trip and pay with cash, either coins or notes. If you notice that the price seems a little hefty, it's because the price includes a S$1 refundable deposit. Make sure you claim the deposit once you exit at your destination. SImply visit the ticketing machines and select the option to claim back your deposit.
If you're travelling alot using public transport, it might be wiser to get a Singapore Tourist Pass rather than an Ez-Link card. The Singapore Tourist Pass, available for purchase from MRT stations like Changi Airport, Orchard, Chinatown, Raffles Place, City Hall, Ang Mo Kio, Harbourfront and Bugis stations. At these stations, you'll pay S$8 per day for a one, two or three-day pass. In addition, there's a S$10 refundable deposit that you'd have to pay. You could, however, buy it online for the same value, but the deposit is not refundable. The amount that you pay for the card allows you to travel on buses and trains for an unlimited number of times.
Save some cash and take the trains and buses and get to see a dose of Singaporean behaviour on public transport while travelling to your next attraction in Singapore.