The carousel is fairly complicated accessibility-wise because it has images, motion (revolving images), text, and links.
Unless your carousel only has 1 image, you need to include at least one of the two options for navigation - arrows and dots.
You can add alternative text to images in the carousel by first clicking the thumbnail in the carousel and then clicking the image itself. For each selected image, use the Alt Text field in the toolbar to enter the alternative text.
If the image includes content not entered into the banner (see the section below), then you must use alternative text. Otherwise, leave the alternative text field blank. If it doubt, it's better to use alternative text than not.
The banner includes text and a button. The button may optionally include a link. When a link is used, the entire banner serves as the link (not just the button). Consequently, all of the text, including any text used in the button, is the link text. This arrangement allows you to use ambiguous text for the button (e.g. learn more), which would normally not be acceptable. However, it is a good practice to always use non-ambiguous text on links and buttons as pictured in the example below.