It's a bit of an involved process and there are several ways to create a landscape, of which the easiest is to make a panorama with the left-hand edge marking due east. This is how I do it most of the time. You can also work it by creating a GPS baseline and calculating azimuth offset from north, which is more accurate.
Click here to read my blog post about creating some recent landscapes; it includes a link to the Stellarium Wiki where you can find more detailed instructions. Getting it into Stellarium is usually just a matter of unzipping the file to your Stellarium Landscapes directory - the location of that may vary depending on your OS; the readme.txt file in the zip file has more details.
Something is not right. This message is just to keep things from messing up down the road