Select the shape tool and press to open the settings.

Choose 'Polygon' from the 'Shape' menu.

Choose 'Solid' from the 'Fill' menu.

When you are finished with these settings, press the 'Done' button.

Press and release the spacebar or to place your first point.

Use to move the cursor, you'll notice a line connecting the previous point and your cursor's current position. Draw another point.

Place another point.

When you are ready to close the polygon place two points in the same spot.

When you do this it will add the final line between the first point and the last point.