Satellite collision avoidance is software that works out when two objects will pass too close in orbit, and plans the move a satellite makes to dodge. It starts from a warning from space situational awareness that two objects may meet.
Objects in orbit move at several kilometres every second, so even a miss of a few hundred metres is close. The software predicts the path of both objects for the next days, and finds the moment when they are closest. It then works out the probability of collision, a number that depends on how accurately the two positions are known. The operator sets a limit. If the probability is above it, the satellite moves.
The dodge is a short burn of the satellite's thrusters, which changes its speed a little. A small change early is enough, because it adds up over the time before the objects meet. The software tests different burns and picks one that clears the other object with the least fuel. It also checks that the new path does not bring the satellite close to a third object.
Take, for example, two working satellites owned by different companies that are predicted to pass 150 metres apart. Debris cannot move, but a satellite can, so both operators could move at once and hit each other's new path. The operators therefore share their plans and agree that only one moves. The software of each company checks the agreed plan against its own prediction before the burn.
As more satellites fly on their own, more of this is being automated, as in levels of autonomy. The same kind of planning is used for drones, which is drone autonomy software. In both cases, a person usually approves the final move. A burn uses fuel, and fuel limits how long a satellite can work. So the operator wants to move only when the risk really calls for it. This is why accurate tracking matters, for Earth observation satellites and for every other satellite.