You have plenty of shortcodes in the list here. Just copy and paste it where you want.
YayMail shortcodes in Shortcodes section
You can see the list of shortcodes here too.
YayMail Shortcodes in editor
When a third party plugin uses WooCommerce order meta to add their information, you can display it in YayMail by going to Shortcode > Order meta.
YayMail Order meta shortcodes

Want custom shortcodes?

You can also create your own shortcodes using filter by adding shortcode name with prefix: yaymail_custom_shortcode_['name'] in file functions.php of your site's theme.
You can see your custom shortcodes in the list here.
YayMail Custom shortcodes
Note: Custom Shortcodes only work in emails when you place an order, not work when send test email.