[Neus]

I'm not really sure how to explain it but I'll do my best. Whatever turf type you're using in the map editor, double click it and it should take you to its definition. (Depending on what it is it'll look like

turf
     atlas
           high
           dense

etc.

Copy and paste that into a new file. If you want the new turf to be dense, indent it under dense, otherwise just put it under the main type (ie 'atlas' in this example).

turf
     atlas
           high
           dense
           my_new_turf
                   icon_state="the icon state to use"
                   Shift_X=8
                   Shift_Y=10
           my_other_new_turf
                   Shift_X=4

Look up in the icon file which icon_state you want to use. You can also get this by editing the turf on the map and seeing what its icon_state var is set to.