OK, first put the camera in AUTO. That will let the camera set the speed, f-stop and ISO to appropriate values to take the photo. You need to spend some time and learn about how to set the correct exposure. That's done with shutter speed, f-stop and ISO settings that are appropriate for the amount of light and the capture you want.
The key is that ALL the factors work together for exposure. Focus is another factor all together. While f-stop does effect the depth of the focus it does not effect the overall focus of the shot.
Sorry, I'm going to have to disagree with Auto mode. You can use Auto all you want, but that auto flash is going to pop up and try to properly compensate. It's really not the right mode for this.
You will want MANUAL mode. Without manual mode, you won't be able to get into Bulb shutter speed on that Nikon 3300.
Use Manual mode, open your aperture to the maximum allowable on the lens, scroll the shutter speed lower and lower as desired, experimenting slo the way. Scrolling slower than 30 seconds should take you to some bulb shutter speed settings. Bulb means, however long you hold the button, the shutter stays open. That could be 2 seconds, or it could be 15 minutes!