What a horary chart is
Horary answers one specific question and is cast for the moment the astrologer understood it. Nobody's birth data is involved: the chart describes the question itself. Three things are needed, the city, the date and the time. The ascendant stands for the querent, and the house matching the topic stands for what is being asked about.
Radicality checks
Before judging, the chart is tested for fitness. A void of course Moon makes no exact aspect before leaving its sign, and the matter usually goes nowhere. Via Combusta, the stretch from 15° Libra to 15° Scorpio, is considered spoiled ground for the Moon. An ascendant in the first three degrees of a sign reads as too early, in the last three as too late.
Houses and significators
The chart uses Regiomontanus houses, as traditional horary does. The querent is taken by the lord of the first house, the quesited by the lord of the house that owns the topic: the second for money, the seventh for a partner or an opponent, the tenth for work and authority. The Moon is always a co-significator. Applying significators give yes, separating ones give no.
Which moment to take
Take the moment the question was voiced and understood, not the moment it first crossed someone's mind. For a letter that is the moment of reading. The place is the astrologer's, not the querent's. This page starts from the current minute and the capital of your language version, and both can be changed.