It sounds like you know how to configure a Map Series, but just not how to configure a Layout for a Map Series which is to have the extent of its Main map frame indicated on its Overview map frame.
The steps that I use to configure a layout for that are:
- Insert a map, which I rename to be Main Map, and configure it with the layers you want
- Insert another map, which I rename to be Overview Map, and configure it with the layers you want
- Insert a layout
- Insert a map frame onto the Layout using Main Map, and rename it to be Main Map Frame
- Insert another map frame onto the Layout using Overview Map, and rename it to be Overview Map Frame
- In the Layout click on the Overview Map Frame to make it active
- On the Insert tab of the Ribbon use the Extent Indicator button to choose the Main Map Frame to be the extent indicated on the Overview Map Frame
- If the rectangle shown on the Overview Map is hard to see use the Map Frame | Format ribbon to change it to something like a Stroke color of Mars Red and a line Width of 2 pts.
This workflow comes from Making Maps and Map Series using ArcGIS Pro Layouts which is an eLearning video course that goes into making various types of map series with main, overview, inset and index maps.
Disclaimer: I am the author and presenter of the course mentioned above.