The answer to the first question can be found here: /topic/2788/
Regarding the second question: gates are located in the objects section, specifically in the "All-terrain objects" tab, and mountains are accordingly located in the tabs corresponding to your terrain type (mountains on grass are in the "grass" tab, for example). You can also create mountains using Tiles by creating irregularities on the surface, painting a different terrain type on them, and marking the result with the mask tool so that such mountains are impassable.