Install automatic1111 web ui for stable diffusion
Input "nude" into the prompt
Okay, more seriously you should probably look up some prompting tutorials. There are plenty of resources out there for instructions on how to get stable diffusion running and use it to get what you want. Using Google will give you faster and often better answers than waiting for someone here.
You can also look at the images generate by users of this site and in most cases see the prompts they used to generate the image. Lot's of interesting prompt ideas to be found here as there are more than 1/2 a million images.