Some examples here. https://support.airtable.com/hc/en-us/articles/218734758-A-beginner-s-guide-to-many-to-many-relationships
Let;'s take the example of products you sell. An order can have multiple products in the same order. But those products can also be connected to multiple orders hence the many to many association.
Here are some real life *-* examples:
Movies and their visitors (or any public event and their visitors for that matter).
Trainers and trainees.
Companies and employees, since an employee can have multiple employers too.
Many to many association
Example : a many-to-many relationship exists between customers and products: customers can purchase various products, and products can be purchased by many customers.
(many customers can buy many products And may products can buy from many customers)