The game is basically nothing but Quests, so there's a structure and progression to them.
As a licensed Courier, you can just take on procedural Courier quests. These earn you money based on how much time it takes to make a delivery and increase your overall Reputation in the area.
If you're doing a Guild-based courier quest, you can take Guild reputation (known as Honor) and a lower amount of money instead. This is important if you're trying to build up goodwill with a particular Guild.
Guild Honor can also be built by doing smaller handcrafted quests for specific members of a Guild. These are short quests and fairly boring, and also don't reward you with money, however they do definitely reward you with more Honor than Courier work would.
You can freehand the economic tasks of the Guild. This will give you some honor and some money, but not a whole lot of either. The work itself is also quite boring. However, on the plus side you don't have to actually go anywhere so these are easier to perform.
Honor allows you to get into higher tiers of quests for that Guild. Generally, once you start doing questlines for a Guild directly, it builds its own Honor -- however if you make decisions that negatively impact the Guild, it won't and may even decrease it. Doing more investigative work into a particular issue can sometimes lead to Honor bonuses if you've helped the Guild more than normal.
Questline Tiers
That said, questlines for a guild follow a predictable pattern:
Primary questlines deal with the city you're in, and all locations will be inside of it.
Secondary questlines deal with cities that are adjacent to the current city.
Tertiary questlines go well outside the bounds of the current region and deal with parts of the Guild more global in scope.
Unlike Courier quests, there are no time limits on Guild questlines. There also tend to be multiple solutions to them, some of which increase Honor more and some which can be very risky for your Honor.
Doing questlines for a guild will increase your reputation with them, allowing additional questlines to unlock.
Through the course of doing questlines, you can decrease your reputation with other guilds. This is repairable by doing more work for them. Sometimes you'll gain reputation with other guilds instead.
However, you can also decrease their power -- if this happens it's irreversible and may lock questlines out, decrease the payment of courier quests, etc. It can have impacts on other questlines as well -- if you weaken Cliff Drillers Inc enough, the Mons Miners United questline to exterminate them will become open quicker.
Completing questlines for a Guild will increase their POWER +1 with each one performed. However there are definite power requirements for certain questlines, so if you decrease their power incidentally you may find yourself locked out of future questlines. As a Guild's power goes up, their courier quests pay more and they also offer more secondary/tertiary courier quests, which pay more by their very nature.
