Select "Polygon" mode from the toolbar. Choose a layer from the layer panel in which to create a new polygon. Left-click at the first vertex of the polygon. Move the mouse to the next vertex and place a new one with a left mouse button click. Move to the next vertex. Depending on the connection mode, the edges created are confined to certain directions. See Basic Editor Options for a detailed description of the modes. Use the "editor options" dialog (F3 shortcut) to change the mode, even during editing.
To temporarily constrain the segment direction, press the Shift or Ctrl key or both while dragging the segment. Shift will apply Manhattan constraints (vertical and horizontal only), Ctrl will allow diagonal directions in addition and pressing Shift+Ctrl will allow all directions.
Double-click at the final point or press the Enter key to finish the polygon. Press the Escape key to cancel the operation. Use the Backspace key to delete the last segment.
While you drag a polygon segment, two edit boxes are shown at the top of the layout view. Press the Tab key to enter these edit boxes. Use the Tab and Shift+Tab keys to navigate between the boxes. You can specify a numerical values for the segment vector here. Pressing the Enter key will apply these relative coordinates and enter a new segment. Pressing the Escape key will leave the edit fields.
A polygon will never be "open": there are always edges connecting the current vertex with the initial one. Depending on the mode, this final connection is either a straight line or a combination of edges. In "diagonal mode", there are manifold possibilities to create a final connection in a more or less smart way. The program uses some heuristics to determine one feasible combination. Although this heuristics is not infinite smart, it should be easy to lead the algorithm to the desired solution, by pointing the mouse into the desired direction.