There are two ways to add images
Images can be added to the media library or uploaded to a page. Images added directly to a page need alt text added on that page using the image block options. Images added to the media library need the attachment details filled out.
1. Import an image into the media library
Depending on the information that’s associated with an image before it’s imported some of the attachment details will be filled in already.

2. Add the image right to the page
Add a block, pick “image”
Images can be added by uploading them, getting them from the Media Library, or linking to them on another site.