Feature images are quite a bit bigger than inline images – so big that we haven't used any on live pages on the main site, though this may change when we get the ability to select different image sizes. For now, as an illustration, there's a feature image at the bottom of this page.
If your page needs a feature image, select Feature image component from options at top of body block.
Put the cursor in the Image field of the Feature image block
then click E in panel at top of text block 
then click the image you want in the ‘Select media to embed’ library so a tick appears on it, then scroll to the bottom of the media library page and click select media.
In the Embed media popup, add alternative text if it isn’t already there
then click Embed.
The selected image will now appear in the feature image block
If the picture you need isn’t in the ‘select image’ library, see Add image to library.
You can also add title, subtitle and body text below a feature image. These fields aren’t mandatory; the image can appear on its own, but if you need some text below it, you can add it here, without needing to open a new text block.
The image below is a feature image without any title, subtitle or body text.
