Why do rashis 5 (Simha) and 11 (Kumbh) have no planet in the exaltation list?
There are only nine planets for twelve rashis, so Simha and Kumbh get no exalted or debilitated planet. A kundli need not have any exalted or debilitated planet, and some have as many as four exalted. The number in a house is its rashi: a 5 means Simha, so Venus there is Venus in Simha; an 11 means Kumbh, so Mercury, the Moon and the Sun there are in Kumbh, and with the Moon there the person's rashi is Kumbh.
Related questions
Besides exaltation, debilitation and degree, how do we judge whether a planet is good or bad, for example in the 6th or 8th house?
The 6th and 8th house rule has not been given yet. The full rules will be taught later using example kundalis of five students. For now judge by exaltation and debilitation; not every 8th-house placement is bad.
Can a person whose Sun is debilitated (neech) have the drawing room in the East?
Yes, with remedies; he will not leave the East unused or build a toilet there. A drawing room is not a permanent seat. Only permanent seating, such as an 8-hour business seat, should not be chosen in the zone of a debilitated planet.
Do the directions of the kundli houses shift when the rashis or planets in them change?
No. The 4th house is always North, the 1st East, the 10th South and the 7th West, with the sub-directions between them. Like water flowing in a river, planets and rashis keep moving, but the direction a house represents stays fixed whichever planet or rashi comes into it.
Does a conjunction (yuti) work only when planets sit together, or also through aspect?
It also works through aspect. Sitting together and an aspect relationship both give the result, so Jupiter aspecting with its 5th, 7th or 9th aspect, or Saturn and Mars with their aspects, also forms the relationship.
Each house of the kundli has a rashi in it. Does the rashi decide the direction?
No, the rashi plays no role here. The 4th house is North, the 1st house East, the 10th house South and the 7th house West, with the sub-directions in between. Real charts are then analysed, five a day from the student group, to decide each person's interior; the key is knowing what to do for exalted planets and what for debilitated ones.
For someone with no astrology background, what does an exalted or debilitated planet mean in practice?
Learn the twelve rashis in order and the rest is simple. If the Sun is written with rashi 1, it is exalted, very powerful, and blesses the house and direction it occupies. If the Sun sits with rashi 7, it is debilitated and very weak; if that falls in the 4th house (North), building a house in that direction ruins the person. Vastu without this is incomplete, which is why even a perfect East-facing house can fail.