Making connections between data tables is at the core of building a database web app. To add a connection field, the first step is to define which data tables you'd like to connect and how you'd like to connect them. For instance:

An example of a connection between 2 data tables would be if we have a list of companies and each company has employees. Our 2 data tables would be:

  1. Companies
  2. Employees

To add a connection here, we would go to the Employees data table and add a connection to the company that each employee works for. Technically, we also could've selected our Companies data table and added a connection from the companies to each employee, but this direction wouldn't be advised since employees are likely to change and come and go while companies generally remain constant. It is far more likely that new employees be added and current employee details be edited than companies being added or edited. Therefore, it makes more sense to add the connection from the employee data table (child item) rather than from the Companies data table (parent item). Generally, it is more advisable to connect the child item to the parent item, rather than vice versa.

Once you add a new connection field, you'll then be able to add and edit employees, view a drop-down of all the companies in the database, and assign employees to particular companies. 

Here is a screenshot of the builder after we've added a connection field to our Employee data table linking our Companies data table:

As you can see, in our Employees data table we now have a connection field to Company. Clicking on that field, you can see that each Employee connects with one Company:

Now, anytime you add a new Employee on the frontend of your app, you'll have a drop-down of all the Companies and you can choose a company to assign to the new employee:

This is why adding a connection field from the Employee data table made more sense than adding the connection from the Company data table- because employees will be added and edited significantly more than companies would be added or edited, so it is more advisable to add the connection from the child item that is more likely to change than from the constant, more stable item.