This mission is where you're introduced to the savoury character called Seth. Whilst Seth's line of work leaves a lot to be desired morally, you need to help him in obtaining the other half of a treasure map that he's so desperately pining after.
So call your horse (if you campfire warped to his location) and follow Seth across the outback to the yellow dot on your map (it's a 5 or so minute ride) at Benedict Point. To grab the attention of the guards, you need to steal one of their horses and have them chase you to give Seth a chance to meet up with his 'friend'.
This is a glorified Wanted tutorial and it shows you how to obtain - and conversely lose - your newly found Wanted status. Ride on the main road until you get outside of the red area on your radar, this means you're out of their line of sight and the red filling your Wanted meter will start to drain away.
Once it's gone; you'll be free to meet back up with Seth at the shack. If the guards spot you at any point when your Wanted meter is draining, it'll refill back up and you'll have to try and lose them again!
Once the cut-scene is over with, follow Seth to the telegraph office and he gives you a pardon letter to remove the bounty for free. We recommend that you don't use the letter now, instead, pay the measly $20 bounty and keep the letter should you need to clear a larger bounty for free later in the game.