Most people starting out with a new DSLR have a standard kit lens. Did you get your camera as part of a set, complete with a lens? Then you have what we call a kit lens. YAY! You're ready to shoot pictures! snap. snap. snap.
So the kit lens is really what we call a beginner lens. Photographers have dubbed them kit lenses because they're often included in kits but you could buy one separately at any time. Kit lenses have lesser build quality that makes them more affordable for beginners. The materials are mostly plastic which also makes them more lightweight. This doesn't mean a kit lens is a bad lens. It is great for someone just starting out. However kit lenses do have their limitations.
One of the biggest issue beginners run into with their kit lens (when they learn to shoot in manual) is the choice of aperture. Kit lenses have an aperture range which means some apertures are only available to shoot when you're using a certain focal length.
What is focal length? It's how much of the image you can fit in the shot. 35mm, 50mm, etc. When you zoom in and out and you can fit more of the image into the shot? That's you changing the focal length. It's your view. That's my best down to earth explanation. In kit lenses the biggest aperture available is usually only useable at something like 18mm which is a pretty wide angle. If you wanted to shoot closer than that (zoom in) you'd find that suddenly you can't shoot the biggest aperture. That's the aperture range.
If you're not sure you have a kit lens just look at the lens barrel. For example, an 18-135mm f/3.5-5.6 lens is a kit lens. The aperture range is listed as f/3.5-f/5.6 meaning, you probably can only shoot with aperture f/3.5 in the 18mm focal length of your lens.
This is one of the most frequently asked questions (and source of irritation) when people start shooting in manual - so I thought a little post that explained why you can't shoot with certain apertures would be helpful. It's not that big of a deal but it can be frustrating when you want to shoot with a certain aperture but suddenly you can't. That's the kit lens limitations for you. But you're just starting out and that's okay.