You can earn gold and achievements through killing other players and playing the mod. Mercenaries is a Mount and Blade: Warband modification that enables you to create a persistent character with certain stats that you can assign yourself.
Hope this is helpful for people new to the mod. I've decided to create this since there's quite often people on the servers asking for advice on basic things like builds or how to equip some items. This is a general beginners guide to Mercenaries mod.