How to Turn On & use 'Bulb' mode in Nikon D3300 DSLR?

I'm new to this DSLR System and don't know the menu etc.
I want to use to Bulb mode.

It appears that you have not yet read your user manual, nor have you moved the shutter speed dial from 1/4000ths second to 30 seconds. The next option is "bulb"

So what I'm saying is that most of the important settings used by a photographers are NOT going to be found in the menu per se. There are buttons on the camera which will allow you to adjust ISO, shutter speed, lens aperture, white balance and pick the shooting mode you wish (Manual "M", Shutter priority "S", Aperture priority "A" or Program "P") If you wish to have the most control over your camera, then shoot it in the "M" mode. If you want to use your find digital SLR as no more than a large P&S camera, then sure, use the "P" mode

Download and read the manual:
http://downloadcenter.nikonimglib.com/en/products/21/D3300.html
If what you seek is not in there, then the functionality does not exist. If Bulb is a requirement, then it would have been a good idea to read the manual BEFORE buying.

Suggest you read pages 108 & 110 of the Reference Manual.

I think you must be in M (manual) mode. Rotate the command dial for the shutter speeds until you see BULB in the LCD screen.

Read your manual.