An app shows on your store in one of two ways, and the app's own instructions say which one it uses:
An app block is a part you place inside a section, such as a reviews widget on the product page. You choose where it goes.
An app embed works on every page without a place of its own, such as a chat button in a corner of the screen, or code you cannot see. You turn it on once.
Install the app from the Shopify App Store first. Its blocks and embeds appear in the editor once it is installed.
Other sections, including the header and the footer, do not take app blocks. An app block goes straight into the section, not inside a Group or Columns block. To put an app block where none of these sections is, add a Section section there and put the app block in it.
An app shows on your store in one of two ways, and the app's own instructions say which one it uses:
An app block is a part you place inside a section, such as a reviews widget on the product page. You choose where it goes.
An app embed works on every page without a place of its own, such as a chat button in a corner of the screen, or code you cannot see. You turn it on once.
Install the app from the Shopify App Store first. Its blocks and embeds appear in the editor once it is installed.
Sections that take app blocks
Section
Where it is
Product information section
The product page
Featured product section
Any page
Section section
Any page
Video section
Any page
Orbit section
Any page
Subscription section
Any page
Contact form section
Any page. The contact page template has one.
Popup section
The Overlays group
Offcanvas drawer section
The Overlays group
Other sections, including the header and the footer, do not take app blocks. An app block goes straight into the section, not inside a Group or Columns block. To put an app block where none of these sections is, add a Section section there and put the app block in it.
Add an app block
In your Shopify admin, go to Online Store.
Next to Checkmate, click Edit theme.
At the top of the editor, select the page the app should be on, such as Products, then Default product.
In the section from the table, click Add block.
In the list that opens, click the Apps tab.
Select the app's block.
Optional. Drag the block to another place in the section's list of blocks.
Click Save.
Turn on an app embed
In your Shopify admin, go to Online Store.
Next to Checkmate, click Edit theme.
In the editor sidebar, click the App embeds icon.
Turn on the switch next to the app.
Click Save.
Shopify's guide to apps in themes has more on both. If an app does not show on your store, see An app doesn't show on my store.