To add on to yrh0413's post as not sure how much TS knows about remotes and bulb mode.
Usually people DO NOT use the built-in shutter button on the camera to do bulb mode exposures. You do that, you will shake, and the camera will tremble along with your shaking. You will end up with blurred pictures.
You can either use a wireless remote (if your camera supports it) or a cable release. For the first, you will have to turn on the wireless capability of your camera. These days, the way to do this is to click the remote once to start the exposure, and then click it again when you want the exposure to end. For the latter, it is basically a switch (similar to how the shutter button is a switch), but it is connected out of the camera body, and thus will not be in contact with the camera body. Thus the shaking scenario does not apply.
For BOTH options, you should be using some kind of timer + mirror-up function so as to minimize camera shake when you trigger. When the mirror swings up, there is a minute amount of vibration. Ensuring this discipline in your longer exposures will result in sharper images in the long run.
The remote with timer than yrh0413 mentions allows the remote to time itself, so that you don't have to keep looking at your stopwatch/wristwatch/iPhone periodically to ensure that you have missed the time to finish your exposure. Some of these also have interval shooting functions (but then some camera also have this function built-in) to allow you to shoot MANY shorter exposure frames. You can then stitch these together with programmes (many available on the net FOC, search for Star Photography Stacking). Short exposure = star moves less, but still moves. Many short exposures stacked = star trails.
Other things to take note:
1) Star photography in Singapore is hard, so I'm not sure where you are shooting this from. There is a load of light pollution, and clear skies are hard to come by. If you point your camera at the sky, the surroundings have to be sufficiently dark so that you don't end up with a whole mass of overexposure. If the sky is full of clouds, you will not get any stars too.
2) Most people like more circular star trails, which have to be centered upon a certain star (North Star, IIRC). Unfortunately Singapore is located on the equator, so IIRC we can only get linear star trails here.
Cheers.
