@madea I'm sorry, I don't have a video. If you really need it, I can make one for you tomorrow before work (have to leave in about 15 minutes). But I made you some pictures I think will help.
1) Let's say we want to have the entire lower right corner open around this staircase
https://i.imgur.com/dPqOja9.png
2) We have to remove the floor in the entire space and replace it all around the staircase in the upper left, upper right ad lower left area. PLUS, because of the bug introduced in the last patch, we have to add the tiles that the staircase 'removes' by placing it. In this picture you can see the edged of the platform around the staircase to where I extended the platform. You can also see the staircase removes the floor there. (I believe this was the step that confused you?)
https://i.imgur.com/eay2EUY.png
3) By then lowering the platform to normal room height, the staircase fully integrates with the floorless area and is fully functional. Fences can be placed if you like. If you were to remove the staircase, you would see that floor appears where the staircase used to be, since you put it there in step 2)
https://i.imgur.com/vgWqCZL.png
Please let me know if you need further explanation or instructions! :)