Milliput is a versatile material that is often used with miniatures to build up a section or fill in a gap but it is just as useful for terrain work. Over on coloureddust.com.pl, part five of their Modeling Materials series focused on Milliput here.
Also, on milliput.com, they have a how to page here.
Finally, on the Scale War Machines YouTube channel, they have a video on How to Use Milliput Putty. Enjoy!