import terrain from Photoshop

Hi All,

I'm new in unity learning , I have downloaded Unity Game Development Essential book and i read in this book that I can make terrain in height map using art package such as photoshop and save it as .RAW file and import it in unity

but i didn't understand that very well , and how can I use this 2D Image in unity , so if any one can help I will be thankful

Thanks in Advance