When someone sends you a tasking, you will have Wilco on OSB 19 (or maybe 20, can't remember for sure) and you will have CNC on OSB 7. Clicking on Wilco means you accept the tasking and the red triangle will appear. Clicking on CNC means you cannot do the tasking and, apparently, the red triangle will not come up or will disappear if it is already on the TAD.
What Olaf is saying is that after he clicks Wilco and does what is tasked to him, he slews the TAD cursor over the red triangle to "hook" it again and then clicks the CNC button to get rid of the red triangle.