How to show a block on the frontend home page only?

Place the block declaration into the view/frontend/layout/cms_index_index.xml file.
See an example from the core’s PayPal module:
https://github.com/magento/magento2/blob/develop/app/code/Magento/Paypal/view/frontend/layout/cms_index_index.xml

The declaration place the PayPal logo and banners on the frontend home page only.

See also:

• How to remove «Report Bugs» link from the admin interface
• How to add a block to a page by a layout directive
• How to change template for a standard block using layout directive action method=‘setTemplate’