How do free transfers work in football?

Related questions

1. Who has won the Champions League the most?
2. Why is Chelsea called Stamford Bridge?
3. Who is Chelsea rival team?
4. How many times have Chelsea won the Premier League?
5. How many trophies have Chelsea won under Abramovich?
6. When was the last time Chelsea won the EPL?
7. How does football club make money?
8. Is Abramovich the sole owner of Chelsea?
9. Why is Chelsea called the blues?
10. Who is the current captain of Chelsea?

Tags

1. #transfer
2. #before
3. #contract
4. #involves
5. #professional
6. #association
7. #expired
8. #available
9. #football
10. #bosman
11. #releasing
12. #known
13. #player