Where it starts to come together

I almost never talk about the 6th house. Not in readings, not in writing, just generally...not. It's situated in between the 5th house, which is romance, creativity, and children, and the 7th house, which is relationships. Once you learn what the 6th house is, you'll probably agree with me that a "who put that there?" is in order. What maniac would situate a house about keeping busy in between the houses of creativity and commitment? Don't get me started on universal design.

Background
As you go around the wheel (counter-clockwise, because that's how astrology works), the bottom 6 houses of your chart (the ones under the horizon), are much more personal and about the private version of you. Once you hit the 7th house, you go public. For example: the 7th house is relationships--the kind of relationships that everyone is aware you are in (if people are not aware, that'd be a 5th house or 12th house matter)--but it also governs legal cases and open enemies. If you have a nemesis, that's a 7th house situation, and everybody knows about it. Often, when something big (Saturn on out) hits your 7th house, that's when you go public with something, or you're just out and about more. Conversely, when something big goes from your 12th house into your 1st house (under the horizon), you become more private.

The 6th house is therefore situated right before you go public. So, think about it this way: what do you need to do before you go out? You get your shit together. You make sure you have your wallet, keys, snacks, water, the right shoes, you look in the mirror, you grab any notes you might need to use to address the public. You prepare. You tinker. Some of you fuss. Public scrutiny can be a gauntlet if you're winging it, but some 6th house and Virgo never stops fussing about what people will think (and delays going public as long as possible, in my experience).

Mental
The 6th house is about synthesis. People without a lot of 6th house or Virgo struggle with answering the question "so what?" The first 6 houses of your chart are about discovery of who you are as a person, and in the 6th house you start to put a bow on yourself so you can present publicly. Similarly, the 6th house helps you add context to the information you're about to tell other people about.

A (mostly-relevant) aside: my favorite thing about the Freedom of Information Act (and a fun fact for most of you today) is that it requires that government agencies produce their documents to show what they're up to, but, legally, the government does not need to explain said documents to you. They just give you what you requested. What are you going to do with raw figures from an EPA water quality report if you're not trained to read the report, you know? Probably draw some weird conclusions without context. In the 6th house you begin to filter what's useful (based on your expertise) and ignore what isn't. You apply knowledge you already have to solve problems. Do you have the knowledge necessary to read the water report? Who do you know who does?

The mutable houses (3, 6, 9, and 12) are mental houses, meaning that their activity is primarily mental in form rather than physically obvious. Seeing a lot of heavy planets in either house 3 or 6 tells me there's stress, mental pressure, depression, compulsive stuff, or sometimes a sense of myopia at play. Charts are NOT diagnostic tools, but they do give you ideas of where to look in terms of pressure sources.

Physical
It's the house linked with digestion (same with Virgo, which is the traditional ruler of the 6th house), in which your body takes the nutrients from everything you just ate and uses that to power you, while getting rid of what it can't use (so you can unfortunately take "get your shit together" very literally, as well, though I prefer not to think about it). Almost like clockwork, people with heavy transits in their 6th house will have dietary issues or go on a crazy diet (depends on what's happening in there). I've also had issues with my teeth when the 6th house is involved in transits, but that might just be me.

Nodes
Personally, I find the case of 12th house south nodes vs. 6th house south nodes fascinating. The south node of the moon is about conditioning, either early this-life or past lives (depending on what you believe), or both, and astrology is a polarity system, so you can learn by studying opposites. In almost all cases of people with 12th house south nodes, there's a flow that they prefer to go with, or heavy religious conditioning limiting personal freedoms, or both. What life likes to do to these people is give them physical symptoms they can't ignore so they have to wake up and go to the doctor and stop just drifting (uncomfortably) through life. They're EXTREMELY accepting people, usually, and they get taken advantage of because they don't pay attention to their internal alarms that something might be amiss, but again, life sends them wake-up calls in the form of assholes to get them to activate and fight back. Life does a lot to try to get these guys to stop flowing and stand up to take care of business (north node/6th house behavior in this case).

Conversely: 6th house south nodes are not reading this. They're sitting back with their arms crossed over their chest, saying "prove it." They are not into the woo. They will not get out of their heads, and will find the flaw in anything, because they spent all last night thinking about it. But don't worry! They're their own worst critic, so that mean shit they said about you is nowhere near as mean as the stuff they tell themselves. Generally speaking, they really need to learn to relax.

It might be worthwhile to just lock people with these opposing lunar node situations in rooms with each other (this is my solution to lots of problems) so they can take turns horrifying each other, or the 6th house south nodes can escort the 12th house south nodes to the doctor and the 12th house south nodes can teach the 6th house south nodes to meditate. 12th house is "I don't see the problem" and 6th house is "I see nothing but problems."

6th house people and things
The 6th house is unequal relationships, which includes coworkers, because you probably have different duties than your coworkers and you're paid different amounts. And for far too much human history, people have had servants or slaves, which would be a 6th house matter (I gotta say it even if I don't like it). Finally, large animals that work for you are also a 6th house matter, so if your car is a horse, that's a 6th house horse.

If you squint, you can see how 6th house scrutiny would apply here: you're likely to be critical of subpar work products of your coworkers, and literature is not exactly rife with examples of positive treatment of servants or slaves. So 6th house can be mildly to extremely unequal.

Usually when I see 6th house activity, my first question is health and my second question is coworkers, but it depends on the age and situation of the person I'm speaking to. Very occasionally do I get to ask about horses.

TLDR
The 6th house isn't sexy, but it is terribly useful. Use the mental image of the inner workings of an analog clock, where all the parts have to function with precision for it to work properly. You can't just throw random parts of a clock together haphazardly and expect to know what time it is, you know?