there are alot of tutorials around on youtube if its easier for you to understand them through that. also there's the tutorial in documentation file here in FH.
technically you make a height map using only black grays and white. the hight map is made with 513x513 pixles. (must be made in something more highteck then ms paint like photoshop or GIMP <---is free) once you make that you will open it in the map maker in the game its under tools-mapmaker.
i hope this kinda helped
im not so good with tutorials.