Anyone is invited to read this post, it should help you to understand the basics and the first steps, as we don't have a dedicated area, although I did suggest it,
I am trying to help and advice members so they can get started, recording they own music on they computers at a reasonably low cost.
OK, first and briefly, the 3 important things that you need to know about soundcards, in NO specific order:
1) sound quality (A/D-D/A converters... how good it sounds when you listen through it, and how good it sounds when you record through it), the determining factor here is usually' the cost.
2) stability (does it crash, is it stable and compatible... ), this, doesn't always relate to the price.
3) versatility (ins/outs connections, type of connections... ), again, this, doesn't always relate to the price.
You could have for example, a great sounding box, expensive, but not stable (crashes etc...), or you could have loads of ins/outs but poor sound quality, and so on...
You haven't mention the budget, so let's assume that all you need is something that serves its purpose.
I am going to recommend the card that I use, it's cheap, stable on my system (OSX) and versatile (it is PC compatible as well), sound quality is brilliant for the money.
Here it is:
http://www.m-audio.com/products/en_us/FireWireSolo-main.html You can plug your mixer/amp output at the back of the card, you can plug headphones as well, it is self powered (Firewire), there is a volume knob that control the headphones as well as the main outputs (which is balanced BTW, a nice feature if you use nearfield monitors that have balanced inputs), so the output can go directly to some powered monitors/speakers, or to one of the stereo inputs on you Hi-Fi amp. It is compatible with Pro-Tools LE as well, and it's probably the BEST for the money, and it will stand up pretty well against other boxes at twice the price.
Then you also have an XLR Mic input with +48V/Phantom power, so you can plug and power those nice condenser mic, as well as using standard dynamic mics...
You also get a Bass/Guitar input, so you plug an record you instrument directly into your computer, as well as being able to listen to it through whatever is connected on the output, Hi/Fi amp, monitors....
This soundcard is a Firewire type and buss powered (NO PSU needed, although some laptops need a PSU, so it comes with one PSU anyway), it also has S/PIDIF (Digital) in/out, that's a VERY GOOD feature and a good way to get a killer setup, here is how:
You can invest in a nice dedicated channel strip/preamp, that has a Digital out option for example, and you can connect it directly to you cheap sound card, while using the better converters form the Channel strip (bass/guitar, mic input)... then you record through it, you get a superior/much better sounding signal.
Saying that, you can always plug a channel strip/preamp that doesn't have a Digital out, it will work fine, but it's just good to know that the option is there.
Same can be done on the way out, for instance, you could get a Focusrite Twin track with the Digital option (in + out) and loop it through the sound card,
so you monitor + record through the Focusrite, by using better converters, there are other options out there of course, but the important thing is to have some
Digital In/Out on the soundcard at least. But for now, let's not get carried away or into greater details, it's just good to know that you can get a superior sounding
system by knowing what to do... cutting corners in a good way.
Once you get the soundcard, come the software...
In short, most people on the forum, or elsewhere, can turn their computer into a project recording studio, and record, edit, mix, master and so on...
The crucial bits are; 1 x computer (obviously), 1 x soundcard, 1 x software, and a way of listening, headphones or amp/monitors...
And one last important point, if you hook up a pair of active/powered monitors on your sound card, you can through away your Hi/Fi! Ia m not joking, you can play all your CDs on your computer, you can convert all your LPs and tapes and get them inside the computer as well, then you can archive them on CD/DVD at a higher quality, while you would convert them into MP3 to save space on the hard drive, for instant playback, if you need the Radio, you can just plug your tuner straight to the soundcard, and that's it, you can even plug the TV if you you have expensive/high quality speakers hooked up on the soundcard. Otherwise, if your Hi/Fi amp + Speakers sound great, simply plug the sound card through it, and you can always get rid of your CD player at least...
I personally don't have Hi/Fi anymore, my whole music collection is on my hard drive inside my computer (always do regular backup though!), it's much more convenient and space saving.