Curved line between symbols. Clicking the left mouse button while drawing the line will change the line shape from concave to convex to straight and will also allow you to change the direction of the line. This will create bend points in the line.
Straight, any orientation
Does not require bend points. You can add bend points by clicking the left mouse button while drawing the line.
Straight orthogonal
To switch direction must have 1 or more bend points.