I'm just trying to learn some new stuff and found this. How can I make that sort of gradient on a custom shape with those smooth edges?
Thanks in advance.
Try experimenting with the Blur Gallery filters in Photoshop - there are several kinds to choose from, such as Tilt Shift, Irish Blur, Path Blur etc.
The examples below began as a simple wave shape over a black background
Here's an example using the Iris Blur tool
You can go crazy with the Path Blur tool