A player who reaches the professional game has usually been coached by several clubs before the one that sells him. Football has a mechanism to pay those earlier clubs.
The problem the rules address
Developing a footballer takes years of facilities, coaching and travel, and most of that cost falls on clubs the player leaves long before he has value.
Without compensation, a small club would be funding the raw material for wealthier clubs and receiving nothing when the investment matured.
The rational response would be to stop developing players altogether, which would concentrate coaching in a handful of academies.
Two separate payments do the work
Training compensation is paid when a young player signs his first professional contract or moves before a certain age. It is calculated from the years he spent at each earlier club.
The solidarity mechanism works differently. When a player transfers for a fee during his contract, a share of that fee is divided among the clubs that trained him between defined ages.
The first is a one-off recognition of development; the second continues to pay out every time the player moves for money.
The amounts are set by category, not by negotiation
Clubs are placed into tiers reflecting their level, and each tier carries a notional annual cost of training a player.
Compensation is then computed from those figures rather than from what the selling club received, which keeps the system predictable and avoids case-by-case disputes.
It also means a modest club can receive a meaningful sum from a transfer it had no part in negotiating.
Why the money often goes unclaimed
Payments are not automatic in practice. A club must know the player moved, know the fee involved, and file a claim within a time limit.
Small clubs frequently lack the administration to track a former junior across borders, and services now exist purely to pursue these claims on their behalf.
What it changes on the ground
The system gives a lower-division or amateur club a financial reason to run a youth section rather than treating it as goodwill.
It also shapes recruitment. Clubs weigh the compensation owed when signing a teenager, which affects the age at which moves happen.
The wider effect is a broader development base, since coaching a child who may leave still carries a claim on his future value.