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

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

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.