If you're new to landscape photography, you may be wondering about filters and their best uses. This great video will give you a look at shooting a real image and using a variety of filters to exactly match the photographer's vision.
Coming to you from Andrew Marr, this helpful video follows him as he shoots a sunrise seascape. In it, he uses a variety of filters, including a neutral density filter, circular polarizer, and hard edge graduated neutral density filter. A neutral density filter is simply one that cuts down on the amount of light entering the lens without (if it's well made) affecting the color, allowing him to shoot at longer shutter speeds to make the water appear smoother. A circular polarizer cuts down on glare both from the water and on wet surfaces as well as the sky, increasing clarity and contrast. Lastly, the graduated filter allows him to bring down the exposure of the sky to help him capture everything in one exposure. As you can see, it's often the case that you'll want to use multiple filters at the same time. They're definitely great items to have in your bag if you're interested in landscape work.
The problem with grads is that you can almost always tell that a grad has been used. The opening image in the video is a good example. Maybe that's what you want, and if so, more power to you.
especially with a hard edge grad. I find it rare that I pull out a hard grad. AND in today's world photogs are leaning more towards bracketing and doing all of this in post anyway