I want to know how to install sfml 2.3 properly in ubuntu 12.04.

From the website, you have 3 options.

The first, using the build in the repositories, doesn't work for you since you're on the old lts and want the newer version of SFML. While, there are certainly valid reasons not to upgrade to the newer Ubuntu lts, if you're able, I'd suggest upgrading to 14.04, if only for access to updated programs, including sfml 2.1 (and lot of other reasons. I mean, it's ostensibly free, so, provided it works with your hardware, why not? I realize the real world has complications though. Maybe it's not your computer alone, maybe it's a work thing, or doesn't work on your hardware, etc. etc).

The second, downloading the premade builds, is actually pretty nice. Everything is built for you. You just unzip and copy the files to your system. If you're still having issues with this route, you may want to narrow your question down to how to use SFML with your IDE/editor of choice.

The last option is building it yourself. Which isn't that much more difficult (if this is your first time building a package like this, it can be confusing, but stick with it and you'll eventually get through it. It eventually becomes rather easy, and if you're going to be programming on Ubuntu, this will decidedly not be the last time you need to build something), but does require you to know how to build it. The sfml page on this is pretty good, but doesn't go into detail on how to install the dependencies, if you're unfamiliar with that (I recommend using something like the synaptic package manager for installing these, but it can be as simple as typing in "sudo apt-get install "name-of-dependency-dev"". But, it's possible to run into some issues if you're not careful. Personally, I like using cmake-gui to run the cmake files, and don't have a lot of experience with the other methods. I won't go into details on this choice, if only because it would take a considerable post to describe properly, and the aforementioned site goes into enough detail. If you did download the SDK and would like help knowing how to build it on Ubuntu, just clarify, and we can try to walk you through it (though, it's the same process for building anything on Ubuntu, and the internet is full of guides on this. Just use the list of dependencies on the sfml site, and any other guide to building an sdk will be sufficient, in all likelihood. I'm genuinely not trying to be snarky or unhelpful. But, it's a complicated process that I wouldn't do any better job explaining than the sfml site, and/or the dozens of people on stack overflow who have answered it).

Anyhow, I recommend you clarify your question a little. Which sfml version did you download, the prebuilt one or the SDK? What have you tried so far, and where exactly are you getting stuck? Are you going to link dynamically or statically? I'll do my best to check back for your clarification (I sometimes forget to follow up though, so my apologies in advance if that's the case ). If you need help building the SDK from scratch, I really do recommend you follow the sfml site's instructions on this, and googling anything they're vague on, and then asking here if you get stuck at any point, with a specific question of how/why you're having trouble building it. It's difficult and confusing at first, but you'll get through it

Edit*

going over your other post, it looks like you may just need to configure code::blocks to find the sfml files properly. You need to make sure to link correctly, and in the project options, make sure you configure which folders code::blocks will look for the libraries and headers.

Anyways, I upgraded my Ubuntu to 14.04, now there is no problem. Strange things happen sometimes.