The whole is greater than the sum of its parts. That, in a nutshell, is the concept of emergence which justifies the existence of macroeconomics as a field of study distinct from microeconomics.
Mainstream economics places great store on ‘microfoundations’, and new classical macroeconomics aims to do away with the macro side of things by assuming that the hyper-rational representative individual or agent is the basic building block of its models.
Complexity and systems theory has a lot to offer those who accept the need for microfoundations in economics, but in a way that macroeconomic objects emerge from them, and cannot be predicted from simply examining a single ‘representative’ micro agent.
If this is the correct way to proceed, then macro objects can be said to emerge from the interactions of micro agents. The latter can be different from one another, in form and behaviour, but still produce an emergent order which can be studied and used to further understanding and inform economic policy.
As micro agents interact and produce coherent macro relations, structures and processes, the latter also act to shape micro-level behaviour. There is thus a two-way interaction between micro and macro, or a micro-macro dynamics.
This video, while not focusing exclusively on economics, covers what is an important part of the nature of the objects studied (ontology) in many strands of heterodox or non-mainstream economics. It touches, simplistically, on the difference between a pure free market and socialist economy, whether such things exist or not, but much of it is useful and is worth a view, keeping economics in mind.
In an economics employing a micro-macro dynamics, the micro agents might be individuals, classes, households or firms, while the macro structures and processes might be the national or international economy.