@Janet -

Yes, you can certainly do this using the line tool (the one that allows you to do arrows or lines). You can start a line from any spot on an object and connect it to another object at any point.

Kiron

@Kiron Bondale 

Thanks so much for your reply - I find this really hit and miss. Sometimes it’ll connect and if I move the shapes the lines stay “stuck” but more often they don’t “stick”.
That’s what prompted me to look for a formal way of adding connection points.

If it’s supposed to work without explicitly adding points, maybe I’ll need to explore why it’s not always happening. 
Thanks again

FWIW, I notice a subtly of this interaction.

I...

1. Create two shapes;
2. Create a line, not connected to anything;
3. On one of the end-points of the line, I click+hold on the white connector.
4. Now, when I drag that connector near the first shape, it snaps to one of the pre-defined connection points on that shape; the connection fills-in, blue.
5. However, if I drag/mouse over to an edge of the shape, the connector snaps to that edge and fills-in blue. The shape’s pre-defined connection points remain white.
6. Also, I’ve noticed that if the line’s connector has snapped to one of the pre-defined connection points (i.e. step 4, above) (or, if I’ve dragged to the center of the shape) if I pause for ~3 seconds (keeping the mouse button held down), the connector unsnaps and more easily can be placed on a spot on the edge of the shape.

Hope that helps!