Hi Joe,
I’ll try to help. I had trouble with this when I started using Bubble too. Specifically the Data Source.
Thing, Data Source, and Type of Content are all related.
First, a Thing is just something in your Database; it’s just type of data. (e.g., a User, a Book, an Order; whatever data types you have defined in your database)
The Data Source says where your app should look for the data. You can store data in different places, and Data Source is how you specify where to look and how to look for it. The where could be your Database (e.g., by doing a Search For), or it could be the data from the parent group, or it could be data stored in an element’s custom state. And the how you find it could be that you do a Search, or you might use data from the Current User, or you might get data from an API call, etc. By combining where to look and how to look, you tell Bubble how to fetch data.
Type of Content specifies what kind of data you want to retrieve from your Data Source. So if you have a repeating group, in which you want to list all Users, your Type of Content would be User, and your Data Source would probably be “Do a Search For” Users. Type of Content can also be non-database objects (i.e., Non-Things) too. It can be a Text, Number, File, etc. Any of the basic Data Types that Bubble provides.
To get your head around the concepts, I’d recommend creating a new custom data type, manually add 4 or 5 elements, and then try to display them in a repeating group. That might help you grok the relationship between Thing, Data Source, and Type of Content.
Let me know if this helps!