This is the URL of the post itself, which you can't get until after you post it. After you make your LJ post, you need to copy the URL of the post and edit the post to put the URL in here. This is the URL of the image used for the improved Graphical LJ-Cut. The reason I call this “improved” is because the image disappears (like the text of a normal LJ-Cut) when you click on it to reveal the hidden content. Optional. You can omit this, or change the text in quotes to anything you'd like. This is the Title text for the LJ-Cut image. This is where the content inside the cut goes. It can include text, images, other HTML; anything you'd put under a normal LJ-Cut.
(This post does not actually contain any NSFW content; that image was from another post in another community.)