Use the works.
Every work in the collection is free for any use, commercial or not, with no attribution required. Do what you like with them.
The model that made them is released under the CreativeML OpenRAIL-M license, which forbids a short list of uses (the license text is linked below). Those restrictions travel with the images. In short: do not use them to harm, harass, or deceive people, and do not use them for the purposes the license names.
The weights are the original Stable Diffusion v1.5 release, kept alive by Deasil.
Downloads include the prompt, seed and settings, so the same picture can be rendered again.