The theory behind Horary is very simple:
1) there is a Question that weighs very heavily on your mind.
2) when you have a clear understanding of what it is that you really want to know, you cast a chart or an astrologer casts one for you
3) That freezes the Planets as they transit the heavens at that moment (hence: Horary)
4) the Rising Sign and Planet that rules the Rising Sign represents you
5) the House, or often more correctly, the Sign that represents the Matter you're asking about and the Planet that rules that Sign represents the Matter. The Matter can be a person or a thing or an idea (like a rumor or a dream).
6) the relationship between those two rulers tells you what has happened, and what is yet to come. That relationship is in the form of aspects. If there are no aspects, then there is nothing to come.
7) the Moon plays a special dual-role signifying the State of Mind of the Querent and also how things play out, how they happen, and when they happen. When there are no aspects formed by the Moon (ie it is Void of Course) then nothing will happen. Note that there are a handful of certain special select Horary Questions where a Void of Course Moon is not relevant. Those are often war, conflict or legal questions, or Questions related to Career.
8) in addition to forming aspects, those Planets must also have Perfect Reception, as opposed to simple Reception. Reception is about "allowing." For example if Mars is applying in aspect to Jupiter, and Jupiter receives Mars then Jupiter is allowing Mars to act. Jupiter is effectively saying, "Go ahead and do that thing that you do." If Jupiter does not receive Mars, then Jupiter is effectively saying, "Go away and leave me alone. Go. Get out of here." If it is a Sign of Enmity, like Mars in Capricorn (the Fall of Jupiter) then Jupiter is effectively saying, "Cease and Desist. I will stop you from doing anything. If necessary, I may even get violent to stop you." And that just might be the case if Jupiter were also in a Violent Sign, otherwise Jupiter would just keep slamming doors in your face.
9) How things actually play out depends a lot on the "strength" of the Planets involved. The strength of the Planets indicates their ability to do act and do things and carry out plans and make things happen. A Planet that is not just in its own Sign, but also in its Triplicity or Term, and is Direct in Motion, Fast in Speed, Angular or Succedent, in Hayz, in a trine aspect with Venus/Jupiter/Sun is very powerful. That's a person with a purpose in life who has both the will and ability to act and make things happen.
A Planet that is Slow in Speed, Retrograde, in Fall/Detriment, Cadent, and not in Sect or worse is Out-of Sect isn't going to be able to do anything, even when there is Perfect Reception in the chart, this person is going to botch every thing up and turn a dream about ponies and gum-drops into a nightmare, because they don't have the strength or will to make things happen.
10) when charts have early/late Ascendants, Void of Course Moons, Moon via Combusta, Saturn in the 1st or 7th House (when not a significator) you can look at the chart for reasons why you are getting those warnings.
Often a non-significator Planet is making an aspect to one of the primary significators. Sextiles and trines usually indicate on-going events which first must be completed before anything can happen. Conjunctions, squares and opposition usually indicate obstacles that are preventing things from happening, and with the "hard" aspects sometimes things can still happen if those obstacles can be overcome.
The condition and placement of the Moon/Ascendant Ruler will tell you the State of Mind and what kind of person the Querent is; good-hearted, or ambivalent, or in sheer terror, in a total panic, has the "stink of desperation" or is immature and selfish, looking do to harm, or is someone you wouldn't let your dog go near. The Planet that is the Quesited/Matter will tell you about them, but not with the same clarity as the Querent. A poorly placed 10th House Ruler might be a job you really don't want, because it ain't all that or isn't what you think it is. A poorly placed 7th House Ruler is someone you might not really want to be with, or something you don't really want to buy and so on.
For a Planet (like the Ascendant Ruler) in Detriment, it is important that it make an aspect to the 1st House (ie it is not inconjunct in the 2nd, 6th, 8th or 12th Houses), and for other significators that it aspect the House it rules. A Planet that is inconjunct to the House it rules can't witness or give testimony to the affairs of that House. That means it cannot control those events, and being weak in Detriment has even less control and less ability to effect outcomes.
