I have created a shape and selected a layer.
In the Edit menu
Define custom shape... is disabled.
Can any one tell what mistake I have made.
Select the path on the canvas with the Direct Selection Tool (white arrow). Define Custom Shape should activate for you then.
You need to create a "Shape layer" or "Work path" to be able to define a custom shape.
1) As first click on rectangle tool and then on shape layers selector
2) After that draw a new layer and click with a right mouse button on that layer. You will see "Define Custom shape" option
3) Or you can create a new layer with a pen tool
4) And then take a "Path selection tool" and right-click this layer