This mission in Red Dead Redemption is only available after Bill Williamson shoots John near Fort Mercer, and Bonnie MacFarlane saves your life.
After talking to Bonnie MacFarlane, you agree on a favor — to help her guard the ranch to pay off the $15 debt spent on your treatment. Head to her house, marked on the map with a blue dot, and accompany her, listening to stories about this settlement. Then watch a cutscene where Bonnie asks you to help watch over the ranch that evening, hoping to catch horse thieves. Saddle up your horse and follow Bonnie to the ranch location. Along the way, you need to shoot rabbits stealing vegetables.
After doing this, saddle up your horse and follow the woman to help her kill coyotes. Note: We advise honing your shooting skills, as coyotes can cause significant damage to the ranch by attacking the chicken coops. Once you do this, continue to follow Bonnie, who will lead you to a small house that will belong to you from now on. Tie your horse to the hitching post and go rest.