Context menu
The command Insert/Line or the matching icon from the icon bar allows you to place lines on your sheet. Click the icon or command, then keep the left mouse button pressed on the sheet and draw a line in the desired length. After releasing the button the line is visible on the sheet. Alter the position by picking up the line with the mouse and pulling it into the new position. Alter angle and size by clicking on one of the blue squares at each end of the line, keeping the left mouse button pressed and moving the box up or down or back and forth.
After releasing the button, the line has a new angle.