Your first Fighters Guild assignment in Firewatch is to escort one of the citizens, Merdon Dillmoon, to The Queen's Cutlass tavern. Head across town to his manor, where he awaits inside. He'll tell you about a few bullies waiting for him in front of the Queen's Cutlass, before following you to the location.
True enough, as you get close to the tavern door you are confronted by two Dunmer men. The leader, Ademnal Lleryn, greets you and makes fun of Dillmoon's "bodyguard", which would be you. Here, your options vary. If your Speechcraft skill is at least 30, you can either return a smart comment, or try to intimidate Lleryn. Otherwise you only have the intimidate option. The smart comment starts a battle of wit and tongue between you and Lleryn in dialogue, which you can ultimately win with a Speechcraft skill of 50 or above. If you do win, Lleryn backs down and lets you through. If at any point you choose "You don't look so tough", Lleryn and his partner attack you. If you can bring Lleryn's health below 30, he'll give up and let you through -- that is, unless you strike a blow that kills him, which means you have to kill his friend as well.
Whatever the outcome, Merdon Dillmoon thanks you upon entering the tavern, leaving you to collect your reward from Brandt. If you talked Lleryn down, you get a reputation point, two Fighters Guild reputation points, 100 gold, a copy of the Hand-to-hand skill book, The Prayers of Baranat, and a 15 point disposition bump with Brandt. If you beat him up without killing him, you get the same reward minus the book, and only a ten point disposition bump, but you gain a reputation point. If you killed Lleryn, Brandt gives you 75 gold and tells you not to be as violent in later assignments; you also only get one guild reputation point. If Merdon somehow died, Brandt expels you from the guild.