Mouse: Control.

Build a bridge and help your workers to get items from the other side of the valley. Start from watching terrain where your bridge will be located. move your mouse to right edge of the screen to scroll the scene. It works in the same way for left edge. Click Design your bridge from the up-left corner of the game. Connectors are lighter and cheaper but your workers cannot step on them so you need to use combination of walk and connector elements. Pick one of the bridge elements from the right side menu. Start building by holding down left mouse button on one of the nodes located below. Move your mouse to place where bridge element should have its end and release left mouse button. If your want to delete a bridge element, just select it and click "Delete selected" from upper-left menu. You can also use delete button from your keyboard. When the bridge is finished click test icon from the upper left menu.