If i buy a nikon d5600, will i not need an intervalometer except if i need to use bulb mode?

Because i heard that it has a built in one

The D5600 has a built-in intervalometer. It is used at all shutter speed settings EXCEPT the bulb setting.

You may want to do some more independent research into how an intervalometer is used.

The bulb setting is used when an exposure of more than 30 seconds is needed. In that case, the photographer holds the shutter release down and uses some kind of timer to measure the exact exposure used. When shooting deep space, it is not unusual for an exposure to be from 3 minutes to as much as 1 hour. Most remote shutter releases allow the photographer to lock the shutter open for these times

Here is a photo that was taken using an intervalometer to produce about 60 sequential images. Those images were then stacked to produce the photo

If you only need to shoot one frame, you can shoot it in Bulb mode without using an intervalometer. If you need to shoot a series of timed shots, then that's when you need the intervalometer. If it has one built-in then good for you!