A video card’s RAM is used only for video games and not for other computations. It is volatile, meaning it forgets information when power goes out. Video cards in a computer typically have anywhere from 2 GB-4 GB of RAM to store graphics data at a time (most notably textures).
The VRAM stores the current screen and any permanent information that changes for every frame (e.g. position of the player). The VRAM on modern graphics cards can be GDDR5, GDDR3 or older DDR3 standard, with the different types differing in their processing rate and power consumption levels. The reason why VRAM needs to stay powered during computing cycles is as follows: When rendering game frames, the program selects an animation frame that it wishes to display, then renders graphics onto the screen. When it is done rendering, it will output this frame for viewing by saving the frame to the VRAM.
Gaming memory is typically DDR3, since GDDR5 would require more power and input/output pins for no gain in performance.