A stock Nvidia card is one manufactured by them. Think of it as an unmodded car. Aftermarket cards from MSI, ASUS or Gigabyte feature better coolers and a small factory overclock.
I have a GTX 970 DirectCU II STRiX. The double cooler only activates when the temperatures go above 70 degrees and even then it is very quiet. It is so good that I've rarely seen it go above 73 degrees. If you want to overclock in the future, you'll need an aftermarket card. Even if you do not want to, they are very silent and efficient.
EDIT: The video Gilrond posted is useful but for a small fee you can avoid the hassle of assembling it yourself by asking the company to do it for you, It's not the most complicated thing in the world but it's not hard to see why it would be intimidating to a newcomer.