Walkhead
The software based guitar amp modeling technology has come a long way, still they are not even remotely close to real life amp. Just having the software will not work at all, you'll need a interface usually called sound card with low latency. Latency in layman term is the time the signal takes from the guitar to the interface/sound card and then to the Operating system, then to the guitar software, then the software convert the signal into the noise,gives it back to the operating system,then it goes back to the sound card, which will eventually go to your speaker/headphone. You see, there is lot of things involved. It is basically converting your magnetic analog signal into digital data, then when it comes out it convert the digital data into analogue noise you hear. This involves time, so if you are using your regular sound card that comes with your computer, you'll hear a delay, you hit a note and it takes few second for your to hear, which is NOT what you want. So the industry has developed standards depending upon what device and Operating system you use. They have made special driver technology which the manufacturer of those interface/sound card can embed with their hardware to work with certain operating system, which is the heart and soul of guitar amp modelling software to work smoothly with no delay. There is ASIO for PC developed originally by Steinberg, Core by Logic (my guess). So you'll have to buy a device with ASIO driver (if you use PC) to get the lowest latency (no delay in what you hear), which comes in various shapes, sizes and features depending upon your need ranging from cheap to ultra expensive. Chances are the sound card that comes with your computer will NOT have a low latency driver. No matter what you buy, it has to have ASIO driver to get the best result. The WaltMart that you've mentioned if it does NOT have ASIO driver, then it is just a rip off. Some cheap products with ASIO driver that you can get that comes right off my head are Behringer, M-Audo and many many more. If you cannot afford any of them, there's a free ASIO driver called ASIO4ALL (google it) that you can install onto your on board computer sound card (some card simply does NOT work, give it a shot) and this will bring down the latency, read their manual to get the optimum speed.
This is just for the sound to work at least in a descent speed. Now when it comes to controlling the software, most manufacturers make their own hardware to control their software like Guitar Rig can be controlled by their own foot pedal (can't remember the name, check their website). These are all based on midi (do a google and learn about it a bit more). simply put the software gives designated number for each control like volume, on/off, preset change, pedal on/off. so you have to have a device to give that special number called midi controller, they come in various shapes from regular looking keyboard to pedal that are for guitarist. You'll have to learn how to program the midi data of the device to the software. The software will usually have a pdf with the midi program/patch change data info, you match it with the foot pedal's data. Then they work.Some basic knowledge of midi will help you a lot for these types of things. Although this guy is officially related to zzsounds.com which is a huge online musical instrument retailer, he does have many good articles that will help you. Make sure to check all the things that he has written about midi, interface and other equipments, of course you might find him a bit irritating with the way he writes.
http://www.tweakheadz.com/
Hope this helps