I know how now!
Go to display settings>wallpaper>lock screen> then select images
you can only make a slideshow for the lock screen sadly:(
Actually, it is true that--at this point--you can only
create the slide show from within the lock screen menu options. (Massive SW oversight by LG.)
However, once you've created the slide show, you can then select it from the charging screen menu options and use it there. (You don't even have to keep using it on your lock screen, because it's already in the phone's memory by then.)
Unfortunately, at least on my phone, the slide show goes so fast (like 2 or 3 pictures per
second), that I'm not so sure I want to use it!
Anyone know how to slow it down?