Graphic rendering is a one of the most processor-intensive tasks on a computer. By adding a video card to your computer you can ease the strain on your processor and speed up your rendering time.
Video cards do their magic by taking the rendering work off of your computer's CPU and handling it independently. This means that your graphics card is dedicated to handling the rendering process while your CPU handles the other processing tasks on your computer.
Video cards are programmed specifically to be optimized for video rendering, pair that with the fact your GPU acts as an additional processor and you may have one of the hottest video editing workstations available.
Your system's RAM can help your processor work more efficiently. By using the temporary memory to process data your computer can handle more things at once. Your video card will also contain its own memory, increasing your overall performance.
In conclusion, making sure you have a high performance graphics card paired with adequate RAM will give you the rendering speed you need to handle your video projects easily.