Scroll down to the bottom of that message where you will find a Sign-in button, then click on it to sign into a Microsoft account.
You will then have an opportunity to describe the image you would like to create using Cocreator.
You can also choose a style for the image from any of the following:
Click on Create to generate the image.
The program will generate several variants from which you may choose. If none of them match the type of image you were looking for, you can modify your description to achieve a result that more closely matches what you hoped to see and then click on the Create button again.
If you like any of the images you see, you can right-click on them and choose Save image.
You will see a count decreasing from an initial value of 50 at the bottom
of the Cocreator window each time you create an image, so it appears you can
only use the feature to create a limited number of images with Cocreator
Preview. You can't specify the size of an image; all images will be created
as 1024 x 1024 images. Below are some images that were created by the program
when I used full moon over treetops for the description with
"photorealistic" for the style.
Below are some images that the program created when I used unicorn
by a willow tree with moon with "photorealistic" for the style. The
tree branches look odd in the first image with one appearing prematurely
truncated. And one "unicorn" has two horns and the eyes look odd to me
in all of the images.
