Let's try an experiment. Find something far away that has lettering on it. Now try to read it. If it is far away enough, and small enough, what did you do? You squinted in order to see it well. What you are doing is forcing your iris to close enough so everything in the distance is in focus. Same as you would if you were shooting a landscape with your camera.
The Aperture of a camera is in the lens. Imagine it as your iris on your eye. If you are in a dark room, your iris opens up to giant size, to allow more light in and lets you see better at night. Go outside on a bright day and your iris will close down to a tiny pinpoint to limit light coming in. This is the same with a camera lens. It is measured by the f-stop, where the oddly named word "stop" is replaced by a number - a fraction of the entire diameter of the lens' iris. Since it is a fraction, as we learned in Mrs. Willis's fifth grade math class, the smaller the number, the bigger it is (1/2 is larger than 1/3).
Each lens has it's own range. For instance, the kit lens that ships with most Canon Rebels have a range of f-3.5 to f-5.6. That means the widest you can open the aperture on it is 3.5, at the cameras widest angle (more on that later). Zoom out from 18mm to 55mm (more on that later), and your maximum is now limited to 5.6. On the other end of the spectrum, the smallest aperture on that lens, regardless of zoom, is f-22. So the wider the angle on that lens, the more light it can let in.
A stronger zoom lens, for the same camera, would be the 55-250mm IS (more on that later), with an aperture range of f-4 to f5.6, meaning the largest aperture that lens can allow is one stop slower (more on that later) then the kit lens. You do give up light when you zoom.
So what is to be done? What if you want to devote your life to Portrait photography? What if you want the eyes of your subject in perfect focus, and have it drop off from there? Well, that is where a faster lens would come in handy. The f-stop (more on that later) range is called the SPEED of the lens. The lower the numbers, the faster the lens. So try a 50mm. f-1.8 lens. This lens is a little more expensive, but will give you a super-shallow depth of field (see Feb 1st post). It will also allow so much more light in that it can drastically alter your shutter speed, but that is for tomorrow.
Until then, homework is: Examine your lens. Lots of numbers and such. Must mean sumptin'.