When planets are either retrograde or combust they are at the extremes in their orbits, relative to the earth.
For example, when planets are retrograde, they are closer to the earth. When planets are combust, they are furthest from the earth, except for Mercury and Venus which can be both retrograde and combust at the same time.
The video below “brings to life” and astrology chart, showing the actual sky reflected in the chart we are looking at.
You can also see easily why I prefer using the South Indian style of chart for Vedic astrology, as it shows the sky correctly, as opposed to other chart styles which are a “representation” of the sky.
When planets are retrograde they become more internal and psychological. The things they rule back-up and make is go inward to get closer to their true essence. This included what the planet rules as a Karakas (natural indicator) and well as what is rules as a house lord. These things get delayed, feel obstructed and are generally confusing.
When planets are combust they are burnt up in the rays of the Sun and feel like a sort of “sunburn”, being pretty touchy and sensitive – that can lead to anger and outbursts. We will have a sensitive spot for that planet based on its nature as a Karaka – often referring back to things from our past or childhood where we were deprived or mistreated. But this is to purify that thing, and focus it with enormous power (related to the Sun) – although we may not enjoy it personally ourselves.