Photoshop :: Creating A Postcard

I created a new file, set my sizes and all that, 8bit and began...I literally am using the line tool to make a straight line vertically, I then want to use my brush at 2pixels and 100 hardness to "stroke path", I set my brush then select path selection tool and right click on the line, but "stroke path"  is grayed out?  I really don't understand.  I am following these directions from a website on how to create postcard back. 
 
this is what i was following:
 
Create a new document with the same exact specifications used earlier for the front. Grab the Line tool and draw a straight vertical line shorter than the postcard’s height, and then place it slightly off center. Set your brush to a size of one or two pixels with a hardness of 100 percent. With the Path Selection tool, right click on the line and choose “Stroke Path.”