Documentation:Embed

Embed (e) at an association end is best explained as "in which table is the foreign key placed". This is often self-evident:

• One-to-Many - foreign key will go in many ends.
• Many-to-Many - foreign key will go into link-class(possibly implicit)
• One-to-One - This is where Embed-flag becomes important because it is optional where to put the foreign key.

If you do not know what end to pick - you can just pick any of them. However, as you grow more experienced, you might want to have the ability to control this.

If you set Embed=false on the many-end, you prevent the framework from doing the reasonable thing. The framework will then assume you have a good reason and create an implicit association class where it can put the keys.