As soon as you arrive in Prosperity, talk to Carmina first. Next, interact with the bag on the table. This will open up the customization screen. You have to set your character’s face and complexion. These choices are final and can’t be modified later.
Next, you can now select your outfit. You can mix-and-match different apparel pieces though some of them will be locked. After you’re done, talk to Kim to get a briefing about the county’s current situation.
After talking to Kim, the mission will be complete. This is where your free-roaming freedom starts. I suggest exploring the immediate areas to get hold of the game mechanics and to get perk points to unlock more abilities for your character. I suggest checking out Prosperity as well.