The South Node in a birth chart
The South Node has no motion of its own: it is always 180 degrees from the North Node, in the opposite sign and, except in the special case of unequal house systems, in the opposite house.
If the North Node is in Aries, the South Node is in Libra; if it is in the 4th house, the South Node occupies the 10th. The two form an axis that is always read together: you understand one only by looking at the other.
Modern astrology sees in it what a person can do without having learned it, the attitudes that come to them on their own and that have worked so far. A South Node in Virgo would give a sense of detail and service, in Sagittarius ease with ideas, in the 7th house a habit of adjusting to others. These facilities are real and precious. Some currents, called karmic, link them to past lives; others see in them simply the legacy of upbringing and background.
The delicate point is the security they provide. You return to them by reflex, even when the situation calls for something else. The work proposed is not to disown these strengths, but to use them as a support to move toward what the North Node indicates. A very organized person, for example, does not have to stop being so: they can put this rigor in the service of a project that is freer, more exposed, or riskier than those they usually choose.