The module allows you to setup a mapping to pull data from an external database into your entities. How and when this happens needs to be developed by you.
The first step is to setup the different table mappings, once you have those you can start the development. There are two main variations that you can use to use the module:
Through a scheduled event, which imports all the tables every night:
Planned import action', this will basically allow you to graphically built the sequence and rollback behavior of the import mappings.
This does the same thing as option 1, but this already has a import sequence built-in and has error handling setup. I would recommend this over building your own scheduled event.
Alternatively you can also do a 'live' import from a datasource microflow. If you use this option make sure you use small sets of data, don't import thousands of records since your application becomes increadibly slow. I've done this myself and was retrieving a few dozen records based on user input and present that in a grid. To built this:
The scenario above also works for both persistent and non-persistent entities