I dont know Nikon lenses, but they seem to be the same sizes as Canon for the most part. Please note the rest of this post is not me trying to act smart, but instead share the way I had to see things in order to understand my tools (cam, lens, etc..)
My kit lens is an 18-55 3.5 but I also have a 50mm 1.8
The 50mm 1.8 is a good portrait lens but can be used for anything, Nikon has one as well. 50mm is a prime lense - no zoom; zoom lenses will have min - max focal length (18-55). Prime lenses cost less b/c no zoom. You can get higher quality lens in a prime for less.
The 1.8 stands for max aperture (diameter for light - smaller number means bigger diameter > diamter of hole = focal length (50mm) divided by aperture (1.8) so smaller number (1.8) lets in morel light than larger number (3.5). Which is why a lense with 1.8 is more expensive than 3.5. Note: the canon 50mm1.8 is unusually cheap b/c its plastic - they have more expensive 50mm1.4 and 50mm1.2
If you notice the zoom lenses might say 3.5-5.6 or something; thats because when you zoom the focal length changes so since the diameter of the hole doesnt change, the ratio must then change.
Example - At 18mm the kit lens can do a max of F3.5. The more you zoom, the higher the F# gets until you are completely zoomed in. So when you get to 55mm the best the lens can do is F5.6.
In addition to light intake, the Aperture also control the depth of field or DOF. Ever seen a picture where the subject is in perfect focus and the background is really really really blurry. Thats what you get from a really small Fstop number like F1.8. The larger diameter hole allows more light in but only one point will be in focus.
The opposite end of the spectrum is a super high Fstop number like F22. That is a super tiny hole but now everything is in super sharp focus because the light rays are concentrated through a small point which flattens the focus of the image. Technically the one point that is focused on, is sill the most focused, but the rest of the image is like 99.999% in focus. This is used for landscapes or anything where you want the entire image in focus.
The reason behind all this is so that you now know how to purchase a lens. There are also other things to consider like Image Stabilization or the speed at which the lens can autofocus.
So now you have to decide what you want to shoot. I got the 50mm 1.8 because I am a hairstylist and want to shoot my clients but this lens is good for almost anything. So since we're indoor the max aperture is important. I need as much light as possible. Also, when shooting people, you want them to be as realistic as possible so wide angle is out of the question and a telephoto would mean that I would have to be 200ft away from the subject. 50mm to 85mm will be where the proportions are perfect. The 85mm will require you to be farther from the subject in order to get everything in the shot, but will also narrow the field so that there is less background.
Think of taking a picture of someone at a party with a pocket cam... You take the first pic with it zoomed out and you get close but you can see half their body and 4 people around them but you cant get any closer to their faces without cutting off their hair or chin.
So what you do you do, you stand back and zoom in. Now you have their whole face in the shot and nothing else at all. This is the effect of a telephoto lens, besides just being able to zoom into something far away.
The last type of lens length is in the 0-35mm(0 is for hypothetical purposes) range which is a wide angle or more commonly referred to as "fisheye" lens. You know this look and while it can create stunning skies and landscapes as well as cool looking automotive shots (almost every rig shot is a wide angle).
This type of lens and macro lenses (specifically for super close up shots), are specialty lenses that will be used rarely compared to others.
Well now that you have a better understanding of your choices, I will give you my personal recommendation since I am in the same boat.
I already have the 50mm so I will go ahead and say its a fantastic lense, the canon version is super cheap ($135 w/ a carrying pouch, 3 lens filters, and cleaning kit - brand new). Everything is in proportion and the 1.8 means great light in dim areas but also really great DOF (sharp subject, blurry background and foreground).
It helps me practice artistic composition, lighting, color, and exposure. Honestly I would recommend the 50mm prime to start with. I do use my kit lens but more for playing with wide angle every now and then.
Con - shooting at one length and with everything in the same proportion can get boring, but its great learning. Not good for all landscape or city skyline, you would want to have some zoom capability because its hard to choose your distance from a subject as large as the land or a city.
The next option is choosing a lens that has similar focal length to the kit lens, but is a proper high quality lens. For Canon I want the 24-70mm F2.8 IS. This will give a little wide angle, great portrait in the 50mm range, and a little more range up to 70mm. However this is super expensive.
Note - F2.8 (lots of light and DOF, IS - image stabilization, + Canon/nikon will use higher quality lens material for something like this , they always do for the 2.8 and lower Fstop lenses.)
You can also look into other manufacturers like Sigma, which will make similar lenses but less expensive, still really good quality. They have a 24-70 F2.8 but no IS, probably doesnt have the expensive crystal lenses and no brand name. But still good lens and at least $500 cheaper.
If it were me... start with 50mm F1.8 Prime lens and learn to shoot with that. Keep using the kit for fun as well, nothing wrong with manual focus. Once you are happy with your shots, (you can post them up here for advice.. check my post a few weeks back) you can look into adding more to the equation like changing up focal length.
Hope this helps. Anyone else, feel free to add anything I forgot.
