In Far Cry 5 you have a huge list of challenges that you can complete, completing these challenges will gives you Perk Points, which you can use to improve your character abilities. These challenges are divided into 4 categories.
Challenges are extremely quick tasks you can undertake as part of Flashpoint or Milestone content. They are designed as something additional for you to complete. These occur in Public Sectors across all four Worlds, as well as within the Crucible.