If you google it, you will find pictures. I would find some for you, but my computer is old and bogs down if I use the Google image search. The soap gets hot and a dark, transluscent spot will form in the middle. That is gel. Ideally, this will spread until the entire loaf is dark and transluscent looking. At this point the soap is very hot and also very liquidy, so I don't recommend moving the mold around!
I, personally, always try to gel. Some soapers try to never gel. Gelling is a chemical reaction. If you gel, your soap will get harder faster. But I wonder if a month or two down the road if there would be a difference in gelled and ungelled soap?