E-R diagram and relationships
You got it right, I think.


$1 : N$ means: Any $A$ may be connected with any number of $B$, but every $B$ is connected to (exactly) one $A$.

Example: (Biological) Mothers and children.
$M : 1$ means the same, just reversed.
$M : N$ means that any $A$ may be connected with any number of $B$ and vice versa.

Example: Teachers and students.