You can visualize it by imagining two rings: 1) the hole in the diaphragm, and 2) the lower esophageal sphincter.
In normal, ring 2 is fixed inside of ring 1, and ring 1 is just big enough to fit ring 2 inside and nothing else.
In sliding hernia, ring 2 is SLIDING above ring 1 as if you are tugging on the esophagus from above. Now you pulled some of the gastric tissue above the diaphragm.
In paraesophageal hernia, ring 2 is still INSIDE of ring 1 (e.g. no sliding), but ring 1 is a lot bigger, so a part of the stomach can fit in ring 1 IN ADDITION to ring 2. This is as if you were trying to push the stomach up from the bottom with one finger - only one part of the stomach is going to be able to herniate above the diaphragm (i.e. you can't push with ONE finger so that you can have gastric tissue on BOTH side of the lower esophageal sphincter and produce a sliding hernia). It's a funny way of thinking about it but hopefully it works.
Now fixed GE junction (ring 2) would mean that you aren't moving ring 2, which would make it a paraesophageal hernia.
