How do I create height maps????

Hi im new to programming open gl and ive only been doing it for five days and i would like to know how to build a heght map so if you know can u tell me

Start your favourite paint program, and create a blank greyscale image. Then take a brush and paint some hills into the picture. Save thge picture into a format you can load, and then load the picture from your program. The image data is the height map.