I'm to buy a lens.but i don't know how to choose?

As i said… I want to buy a lens for my nikon d5100 but i don't know how to choose… Can you help me how to understand all the lenses that nikon or canon has? =\ sorry newbie here

Added (1). Ohh. I forgot to tell well i used to go and shoot @ concert, family occasion, animals and views… Now i only have the 18-55mm f/3.5-5.6 AF-S DX VR Nikkor Zoom Lens which is good… But when it comes to concert ('cause sometimes i'm too far away and i can't take a good photo(s. And animals (birds, insects, cats, dogs, etc that you want to take a picture without distracting so you need to take in long distance to have a good photo(s) too).

Go on the nikon website and look up their lenses. Check out the user comments and choose the one that will do what it is you are looking to do.

What do you plan to shoot?

For the past what, 6 years, maybe, I've used nothing but an 18-200mmG VR (first gen, on my fourth Nikon body) for everything. I shoot mostly landscapes, some band gigs, few portraits. One lens for all. Back in my film days, I had four lenses for my OM-1n and OM-10 bodies. No more. I don't even carry a bag, unless I'm traveling several days or more.

I have two lenses; one is 55-200 and one is 18-55. I'm extremely jealous of 'Y U So STUPID' for having an 18-200 and would strongly recommend getting one like that. It is great for taking photos up close and far away as well. I use Nikon and both my lenses have automatic and manual focus as well as VR which I would also recommend! A lens is a personal opinion, but getting a lens 18-200 certainly covers a lot of ground. Hope I helped!

What kind of pictures are you wanting now, that you are not getting, and what kind of lens will let you get, what you are not getting?
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I too have a 18~200 Nikon DX lens and yes, it stays on one of my cameras a lot. It IS a very versatile lens, however, I also have many other Nikkor lenses from 16mm rectilinear fish eye to 500mm, many are primes. Nothing beats using a true macro for that close up shot or a deep telephoto for nature.
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However, base your needs on your real physical wants so your lens choice compliments you and your shooting style.

There's some real mis-information here, a wide range zoom has so many compromises in design the first of which is aperture, but there's also distortion at all focal lengths and the complete lack of flat field (in focus from corner to corner).It's like a Swiss Army knife, has all the tools none of them work properly. They are newbie traps.

There are plenty of ways of getting good Macro images without going to the expense of buying a Macro lens, bellows or extension rings to name just two. A cheap set of bellows bought off eBay and a Canon FD mount 50mm f1.8 lens, and an adapter to fit the lens to the bellows and on to fit the bellows to your camera, and you have a combination that will have a wider aperture (easier for focusing) and better image quality most Macro lenses all for less than $100. The Canon FD lens because it can't be used on modern Canon EOS digital cameras there are plenty around, they are cheap and they have good image quality.

They are right when they say only buy a lens you have a need for, you find out which lenses you need by using the kit lens (cheapest, most useful option).

No need to apologize. It's a tough question to answer quickly, especially without knowing what you want to shoot. What you shoot determines what you need. I see people are suggesting that you buy a zoom lens which covers everything. Like someone else noted, that's not a smart move. If you want to take really nice shots you need good lenses and they are not cheap. You might consider a 24mm or 28mm prime (fixed) lens and then something like an 85mm and something closer to 200mm. You can buy a cheap zoom that covers all of that range but it's not going to be good. If you need just one zoom I suggest you try something like 24-70mm or around that. Don't buy something that goes from like 18-300. If you repost with what you wish to do you will get better responses.

1- What type of photography do you do?
Lenses are very situational and so I need to know the typical situation you shoot in to offer any adice.

2- What lenses do you currently have.
If I don;t know what you currently have, I can't suggest what to get to fill any gaps.

3- Why in the hell would you care about Canon lenses when you have a Nikon camera… They are NOT compatible.

4- What's your budget
I could recommend you a 2600$ lens but if your budget is only 800$ then that changes things.

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You didn;t specify your budget but here are my suggestions. 24-70 f2.8 and a 70-200 f2.8.