Bound App is a setting that allows you to bind items of one app to another one. To do this, a property of the App or Arbitrary app type is added to the form of the parent app, in which the child app is selected.
Child app items are specified or created on the parent item page. The child entry is only saved when the parent item is saved.
Let's see how the Bound App setting works, taking as an example the Contact and the Supplementary Agreement apps.
Supplementary agreements are always created under a specific contract. Therefore, the Contract is a parent app, and the Supplementary Agreement is a child or dependent app. In order to avoid confusion, the child app item should be saved after the main document (contract) has already been entered into the system. This can be easily done using the Bound App setting.
Bind apps
To create a bound app and bind two apps to each other:
Step 1. Open the form of the Contract app and add an App type field to it. In the field settings, select Supplementary Agreement and select the Bound App option. 
Step 2. Now open the form of the Supplemental Agreement app. Add an App type field to the form. In the field settings, select the Contract app. Please note that if you're working in the advanced mode, the Contract field should be added to the Create tab.
Working with bound apps
Add a new Contract item. To do this, in the right upper corner of the app page click the +Contract button.
The creation form will open, on which you will see the Additional Agreement field.
Click the Create button to open a creation form for a new Supplementary Agreement.
The Contract field is not editable. It will be filled automatically after the contract is saved in the system.
Fill out all fields and click Save. The system will create a new Supplementary Agreement bound to the contract. It will be saved in BRIX only after you save the contract, and will also be added to the contract page.
Please note that if you later delete the supplemental agreement, it will be deleted from the contract page, too.