If you want to make an app available to a site without requiring users to install it, you can deploy it by following these steps:

1. While logged in as an administrator, navigate to the App Catalog site.
2. Select Site contents. If your site collection has been upgraded to the modern libraries and lists display, select the Return to classic SharePoint link.

3. Select the ellipsis (...) next to the app you wish to deploy and select the ellipsis (...) in the popup window. Select Deployment from the menu:

4. Enter the full URL of the site collections to deploy the app to and click Add. Under Available managed paths, select the managed paths to deploy to and click Add >. Under Available site templates, select the templates to deploy to and click Add >. Then, click OK:

5. Select Trust It to complete the deployment:

The app will now show up in the site's contents for the site and can be accessed. If the app contains a web part, you may also be able to add it to a site's page. If the app contains a web part that can be deployed on a page, you may need to consult the app's administrator guide for further configuration instructions.