Is zooming the only way to change aperture?

Sorry if this sounds like a really stupid question… I'm just really confused.
I have a Nikon D50 and the little screen on top shows me the f number… F/stop, is that what it is? Anyways, I just have the 18-55mm lens that came with this camera. When I'm at 18mm it's f/3.5, and increases all the way to f/5.6 at 55mm… A smaller number means a larger aperture, which means more light, right? So, is it possible to get a smaller f/stop than 5.6 when I'm zoomed in at 55mm?

No. Your 18-55mm f3.5-5.6 zoom lens is a variable aperture lens. At 18mm its maximum aperture is f3.5. At 55mm its maximum aperture is f5.6. The only way to get a larger aperture at 55mm is to invest in the Nikon AF-S 17-55mm f2.8G ED-IF zoom whose maximum aperture is f2.8 across the entire zoom range from 17mm to 55mm. About $1, 419.00.

Or, you could just buy the Nikon AF-S 50mm f1.8G prime lens which is only $216.95. Of course it isn't a zoom lens but its certainly better in low-light situations. Since it isn't a zoom you'll have to do what we did back before zoom lenses were invented. To get less in a scene you walk closer. To get more in a scene you walk backwards.

Nope, you can't.f/5.6 is the maximum at that focal length. That's just the limitation of the lens.

If you want a wider aperture while zoomed out, you're gonna have to buy a better lens.

What you have is a variable aperture zoom lens. The aperture changes when you zoom in and out. That is not the control for aperture size. You normally use the wheel to change it. Read the manual on how to do it in the different modes. Yes, you got it right. The smaller the f/number, the larger the hole, allowing more light in. The problem with variable aperture zoom lenses is that maximum aperture size also changes so at 55mm, your lens can only go up to f/5.6 while at 18mm, it can go to as wide as f/3.5. There are constant aperture zoom lenses that do not change aperture size when zooming in and out. They are considerably more expensive. Then there are single focal length lenses, those that do not zoom, that have much lower f/numbers which may further cost more.

Your kit lens has a variable minimum (wide) aperture it's that minimum that changes when you zoom on this type of lens.

If you set your D50 into it's Aperture Priority mode, you can then adjust the aperture to wider and lower using the rotating wheel placed just above where your right thumb should sit when holding the camera. Using the control wheel to change the aperture will be limited by the minimum and maximum apertures available.

Reading the manual should open your eyes to a whole heap of other great abilities your camera possesses

Use manual mode on your camera then change it. If you don't know how learn how or sell your camera and get a point and shoot camera. There's a reason the dslr cameras have more than auto mode.