How to create a quick grid of guides in Photoshop if you are using earlier versions where there is only the 'new guide' command available in the video and missing the superior layout feature such as in CS6 etc
You can use the new guide option and that has horizontal as well as vertical option and a position. Make certain the show guides is on via view menu (this should be the default) and then go to view menu and the new command
You may like to set up a customization for the menu command and add a shortcut (I often use cmd / ctrl 0 but that is also something else).
Once you have done that, repeat that command for the vertical and each time change the position value from 0 to 100 and 200 and 300 and 400 etc and then repeat that with the horizontal. You can then very quickly create a set of guides / grid that can be moved via the move tool and well as clear command in the view menu. It does not need to be 100, 200 etc it could be 50, 100, 150 or 200, 400 etc