I know I am not that young anymore, but please refrain from calling me Sir...
(though it was appreciated).
108-137MHz is the VHF airband.
Connecting an external antenna to your scanner can be anything from a small to a huge improvement, it mainly depends on how high and unobstructed your external antenna will be.
To make a comparison, imagine that your antenna are your eyes and that you are hoping to see as much light sources as far away as possible.
If you can find a junk external FM
(radio) antenna somewhere, you got what you are looking for.
If not, an old Band I TV
antenna would be fine as well.
If you find one or the other, remove any "parasitic" elements it could have on its "boom" (the spine of the skeleton), and keep only the one where the antenna cable connects to. (keep the boom and the bracket)
Mount your antenna vertically (the element to which the cable connects has to be in the vertical plane), bring down your cable and mount a BNC male connector at the end. (if unsure how to do, ask a ham operator or anyone with minimum knowledge)
If you prefer the "off the shelf" solution, look for a simple "quarter wave" antenna (it should be about 60cm / 2ft high)