Look at how other people have drawn hills and try copying them on a separate piece of paper until you find a style that works! It's a little too simple to do a proper tutorial for... it's either just an upside down U shape with some shading on one side, or an upside down U shape except a bit more peaky, with an S shape to indicate the outflow of the dune. And when I say a U, it's a bit more spread out than a U, imagine if you filled a U up with sand and now it's bulging kind of.

Much simpler than a mountain, you only do one shading bit on most hills, and the only difference between a hill and a dune is that a dune has a curved peak instead of a rounded top, and a dune's shading will be more of an S.