I've been through all the posts about rounded corners and Bezier curves, but I'm still stumped:

How do I draw a line with angles, that has straight line segments and rounded corners at the angles? I used the Polygon curve tool to make an "open ended" polygon. But in Format > Position and Size > Slant & Corner Radius, Corner radius is dimmed. (Please see my attachment.)

The simplest example is drawing an "L" shaped line, with the corner rounded to, say, 0.25". More complex is a zig-zag line with straight segments but rounded corners at the angles - not necessarily 45 degrees.

I'm sure the answer is Bezier curves, but I'm too dimwitted to make the Edit Points tools work. When I move the Bezier handles, everything goes into cattywampus "S" curves.

Any help would be most appreciated.