Working with relationships and external collections is a little trickier than relationships in normal collections, but you can achieve what you're trying to do using lists and filters.
For example, you may have two tables in Airtable, Trips and Activities, each set up as their own external collection in Adalo. The home screen of your app could have a list of Trips, and clicking on a Trip could take you to a Trip details screen, where you want to display the Trip Name and Description, along with all of the activities for the Trip. And in Airtable, each Activity record in associated with a Trip Record.
To display only the Activities that belong to the Current Trip on the Trip Details screen, you would add a filter to your Activities List that looks like this:
Basically this filter is saying only include activities where the name of the related trip in Airtable is the same as the name of the Current Trip that the user clicked on from trips list on the home screen.