You asked about Agile, but I will talk about Scrum instead, because I am more familiar with it.
https://scrumguides.org/scrum-guide.html
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Selected quotes:
> Scrum Teams are cross-functional, meaning the members have all the skills necessary to create value each Sprint. They are also self-managing, meaning they internally decide who does what, when, and how.
> During the Sprint: No changes are made that would endanger the Sprint Goal;
> The Daily Scrum is a 15-minute event
A short version is that you have a small team of intelligent people who are given sufficient autonomy. They split time into intervals called "sprints", each sprint is 2-4 weeks long. (If you have no experience with Scrum, start with 2 weeks. When you get used to it, the team can decide the correct length.)
At the beginning of the sprint, the developers and the representative of the customer agree what gets done. During the sprint, the developers do it. Every day there is a short meeting in the morning, when developers say "I completed this; I am going to work on this; I am blocked by this", nothing more.
At the end of the sprint, developers show the implemented changes to the representative of the customer. Then the developers talk among themselves about what was good during this sprint, what was bad, and what they want to do differently the next time.
The important thing (ignored at almost all companies pretending to do Scrum) is that in this ideal world, managers do not exist. Developers manage themselves. In the daily meetings, developers report their progress to each other. What needs to be done, is decided by the representative of the customer (literally a person from a different company, or from a different department if this is an internal project). How it gets done, that is decided by the developers. When developers talk about what was good and bad, and what needs to be done differently, they actually have the power to do it differently the next time. Developers assign the work between themselves, and make estimates how long something would take.
Shortly: the developers are treated as adults, and their responsibility to the customer is defined on a biweekly or monthly basis.