Simply put, a video card improves a computer's ability to render complex, animated imagery. It does this by reducing the strain placed on the computer's integrated components. When a video card is working effectively, the computer's memory and Central Processing Unit (CPU) are free to focus their energy on other important tasks. This improves the functioning of graphics intensive software, such as video games, 3D simulations, and graphics design programs. Most computers purchased from a store are capable of running some of these types of software already, but users may discover that the computer will begin to bog down if they try to run increasingly complex programs. This problem can often be solved, however, by installing a more powerful video card.
No one video card is perfect for every purpose. Therefore, to choose the right card, one's own specific needs should be considered. To choose the right card for a given need, there are five basic factors to be considered: physical compatibility with the computer, GPU speed, on-board memory, the user interface (BIOS), and the price.
The first thing to check is the physical compatibility. If the card being considered will not work with the intended computer, everything else is irrelevant. Most computer motherboards have some type of port for graphics cards. There are several types, with the most common being PCIe, AGP, and PCI. Identify which type of card port your computer has by looking in the owner's manual, or by doing a search online for your computer model. Some computers will have more than one type of card port, offering the user a greater degree of choice. Having identified the type of motherboard interface on the target computer, look at the specs of the video cards you are considering and identify which ones are compatible.
The most crucial hardware components of a video card are the Graphics Processing Unit (GPU) and the on-board memory (RAM). The GPU is a microprocessor dedicated specifically to rendering graphics. GPUs are rated by "clock speed" which is now typically expressed in gigahertz. GPUs with a faster clock speed are capable of processing imagery more rapidly that those with slower clock speeds. Most modern video cards also include their own dedicated RAM, freeing up the computer's main RAM. Generally speaking, more RAM is better, but beware of cards that boast larger amounts of low quality RAM just to print a higher number on the box. If your computer is well stocked with high-end RAM, the amount of RAM on the video card should become less of a priority.
The BIOS is the firmware installed on the video card. Depending on your purpose, you may want to look for cards that advertise a user friendly BIOS interface, which makes it easier for users to change important settings, including the clock speed. This gives users an added amount of room to grow over time. However, users should thoroughly research the pros and cons of "overclocking" before changing these settings. Push it too far, and you could either burn out the card, or overheat your whole computer.
Price is the point that requires the least explanation. Generally speaking, more money will buy a better, more powerful card. At the same time, every customer has their own budget to consider. Keep in mind that while a new video card may seem expensive, it is a lot cheaper than buying a new computer. As a general rule, avoid buying the very newest, most expensive video cards, as their price will likely drop within a few months, and the previous generation will often be only a little less powerful and a lot cheaper.