Insert Mode

On the Design tab, in the Edit Mode group: Click Insert Mode to toggle Insert Points mode on and off.

Note that you can toggle snapping on and off using the I key. You can also Move String Points by simply"dragging" them to a new position in the display.

When Insert Mode is enabled and you move the mouse to insert a point on a string, the cursor will change to a crosshair cursor. Click on the string to insert a new point, then drag the point to a new location and insert more points as required.

Position the mouse cursor over the segment where you want to add a new point.

Click the mouse. You can move the inserted point by dragging the mouse before releasing the button. 

When a string is selected, you can also insert multiple points at a specified interval by choosing Insert Points from the right-click menu.

You can also delete the points on a string from the ribbon or the right-click menu. See: Delete Point