how to make a file a .png to be used for the L.I.E?

in The Commons
I did this before and I know how to use the LIE but I really forgot the process on how you actually get a normal jpeg image the right format to make it so there is no background with it on the LIE when placing it. Could someone give me a quick rundown on how to do this again with an image? would be greatly appreciated.
Comments
You don't necessarily have to use a PNG, just create a mask image that's black where you want the layer hidden and white (or grey) where you want it to show, then load the main image as a layer, select it, click the + to add a new item and select the Mask option, then assign the mask image as its resoruce.
hmm ok sounds more complicated than I remember any chance you could do a brief pic tutorial for this? it would help a lot.
Here is a link to my thread where I made a tutorial about LIE maps
https://www.daz3d.com/forums/discussion/comment/3591981/#Comment_3591981