How to transparent an image in adobe photoshop?

*browse an image
*select the image using rectangular marquee tool as shown in fig 124.

 

*open new file, file<<open<<4x6, you can choose any dimension according to ur choise. Take background colour according to ur choise.
*press ctrl and drag drop the image on the new blank image. Now ur image is look like( fig 125)

 

* press ctrl+T and resize the selected image.
*change the fill value in the fill option as pointed by the arrow. And you get the transparent image as shown in fig 126.