A really sharp, dark and intense cut crease is a great look, much favoured by the Kardashians et al. If you have tried to get this look you will have discovered how difficult it is to achieve.
You need a really steady hand and being able to create a perfect curve freehand is very difficult.
But there is an easy way. You need to find a circular item that, using the upper hemisphere only, is the correct size to fit into the deepest curve of your eye socket curve. Suggestions for this item include coins and bottle bottle caps. It is worth taking the time to find something that fits exactly.
The first step is to cover your entire eye area with your base eye shadow shade. Then apply the shade you want on the lid up to and just slightly over the socket line. Then apply your highligher shade from the socket to the brow line.
Then take your circular stencil item and place the upper hemisphere into the socket line. Take your dark shade and apply to the area above the circle. Blending into the highlighter shade and flicking up or blending out at the outer corner as you prefer.
This will give you a crisp, sharp cut crease exactly in your socket line.
Give it a try and keep your circle stencil in a safe place so it does not get chucked out accidentally.