How an ND graduated filter works
A graduated filter works by only part of the filter being filled in. One side of the line is clear and the other is the neutral density part. To give yourself more options, you can also get soft grads or hard grads. A soft grad is where the transition between the filter and clear part are more gradual; on a hard grad, the line between the filter and the clear part is less transitional. You might use a hard grad if you have a
very straight horizon or want a distinctive line between the sky and the land.
Graduated filters also come in different strengths and the system is designed so you can stack them on top of each other if your darkest filter is not dark enough. If you want to take your landscape photography to the next level, investing in an ND graduated filter system is a great start.
Move ND grad up and down to line up the transition line to the horizon