In Red Dead Redemption 2 you have to find an Point of Interest, you need this task to get 100% completion. This tutorial will show you where to find an interesting place in RDR2.
There are several interesting places to discover, to update the progress we go to the “Mysterious Home” to the north of the map (East of Donner Falls). There you will find a hut, examine the hut by holding triangle (PS4) / Y (XB1).
You can go to Chapter 2 after this chapter.
That's all you need to complete this with your 100% completion.