Once you have Sintel Forms installed on your environment (Office 365), you can add it to any site using the following steps:
- Open Site Contents.
- Click on "add an app".
If you are using the new "Modern Experience" in SharePoint it looks a little different as shown.
- Search for "Sintel Forms" and once you find the app click on it to add it.
- Click Trust It when asked to complete the deployment.
- The installation will proceed and once it's completed you will see the Sintel Forms App appear in the site.
If you are using the new "Modern Experience" in SharePoint it looks a little different and the app will appear in the site contents as shown.
If you are using Sintel Forms On-prem you simply need to activate the Sintel Forms feature within your site.