Adding alternative text to images not only makes your website more accessible for everyone (e.g., people using screen readers) but also helps search engines understand your page content better. There are two ways to add alt text:

Open the media library and open the details of the preferred image file:

Insert the description of the image, and save it:

Voilà 🎉

Click on the preferred image element and click Change image. In the image settings, find the Alt text field, and insert a description of the image there:

NOTE: If you run an online store, the product title is used as the alt text for the main product image by default: