How do lenses work on DSLRs?

I know that typically DSLRs such as the EOS cameras from canon and the nikon 'd' series come with an 18-55 mm lens. I also know what a fish eye lens is but I'm kind of confused what a telephoto, wide, macro and prime lens is. Also, I'm kind of confused… Is there just one 18-55 mm lens? Or is there one for all of those different lenses? (like a 18-55 macro, telephoto etc.) I'm looking to get a canon t3i but I'm clueless. I love photography and editing and all those things but I haven't really graduated from my iphone camera, so I'm unsure what lenses are best for me. ALSO, if you could dumb it down a bit haha? I'm 13. I don't really know a ton of photography terms.

Each lens has a "focal length" which is measured in millimetres. The longer the focal length, the more zoomed-in and magnified the picture becomes. The shorter the focal length, the wider the view and the more stuff you get in. That's the basic fact… Everything is based on that. Let me explain…

A telephoto lens has a long focal length (like 200mm) and zooms in a lot on objects in the distance.

A wide-angle lens has a short focal length (like 18mm) and has a wide angle of view.

A fisheye is just a super-wide-angle lens with a focal length like 8mm. Its field if view is so wide that it gets in everything 180 degrees around it.

One category you missed is called a "normal" lens, and is somewhere between a wide angle and a telephoto. The lens in your iPhone is a normal lens.

A macro lens is a special kind of normal or telephoto lens that allows you to focus on things very close to the lens, so you get a close-up.

A prime lens is a lens whose focal length is fixed - such as the lens in your iPhone. It can't zoom in and out. The opposite of a prime lens is a zoom lens, which can vary its focal length and zoom in and out. The 18-55mm lens you mentioned is a zoom lens as it can vary between 18mm (wide angle) to 55mm (medium telephoto). And of course, in the middle of the range, around 35mm, it covers normal too.

So if you get a T3i with the 18-55mm lens, this is the ideal starter lens (and that's why it's bundled). You'll be able to zoom in and out, cover wide angle to medium telephoto shots which should cover 90% of your needs. In the future you will soon figure out whether you are frustrated at not being able to zoom in enough, or not being able to zoom out enough - and then you can buy more lenses!

For now, I hope this is enough advice to get you started. Have fun!

Every lens has a focal length, wich tells you how wide or narrow point of view it has (actually it is the distance from the sensor to the diafragm); a fix focal length lens is called prime, a variable one zoom. Wide angles give you a wide view and they are in the range from 8-16-28-35 mm, 50mm focal length is usually stablished as the standard view, close to how our eyes perceive things; telelenses give you a narrow view and they are from 80 to about 300 mm, longer than that are very long telephoto lenses.
Cameras having a smaller sensor than what corresponds to a 35 mm film one give you a narrower view when you use lenses designed for the full frame ones, so you have to multiply the focal length of your lens by a multiplying factor to get the equivalent focal length

Your cameras was sold as kit. The kit includes the camera body and a lens. The lens that is shipped in the kit is called a kit lens. What is significant is the focal length of lens. This value tells us if the view it will provide will be wide-angle - normal - telephoto. Your lens has a variable focal length. We call this a zoom lens. When set to minimum zoom which is 18mm, the view will be wide-angle. When set to maximum zoom 55mm the lens delivers a magnified or telephoto view. When set to the middle of this range the view is said to be "normal".

For your camera, setting the lens to the middle of its range is approximately 35mm and this setting delivers a "normal".

The lens you already own is a good start. Don't worry about buying additional lenses just yet. Practice with what you have. You will be learning as you go. At some future date you will be better able to select additional lens.

A wide-angle is a lens starts 70% of normal thus for your camera its 25mm or shorter. The shorter, the more wide-angle. Telephoto is 150% of normal or longer. For your camera this is 55.In other words, The lens you have covers the range of moderate wide-angle, normal, and moderate telephoto.
A macro lens is optimized to do extreme close-up work.