I am not much of a designer. Looks like a very basic thing to do but i don't know how to do it. I just want to create a line that is blurred from the ends and have this shade at the bottom of it. Its a kind of a separator that i can use on a website. I want to do it in Photoshop. As an example, check out the following image:
Make a rectangular shape of the total size of your line (e.g. 1px by 600px). Set fill to 0%. Double click the layer to access the layer styles. Add gradient overlay. Edit gradient to go from 0% black to 50% black to 90% black.
I'm doing a straight line (in Illustrator) with faded edges and I just selected a Variable width profile setting next to the stroke setting
(Not sure if this would be relevant for a curved line or shape though)
Photoshop is a lot easier - I add a layer mask and apply gradients to the edges
I would practically never use the eraser tool as it's a destructive edit.
If you use layer masks you can always change it later