Entity-Relationship Conceptual Data Model
Green rectangles are tables, red eclipses are attributes, blue triangles are tables that connect tables and a relationship descriptors so you could understand their relationship. Do not name triangle like tables as referred on the diagram, such as 'contains' , give them meaningful names.

Purple eclipses are additional attributes of tables that connect other tables

Numbers and letters next to triangles are telling you what kind of relationship it is

Whether is :

One to many - example Table Account has 1 and table Character has N which means one account can have many characters , but character can have only 1 account

Many to many - example Character can "Ran into" many creeps and many creeps can ran into many characters

What does it means? 

It means that depending on a relationship type, you will create foreign keys and constrains accordingly. If you are still in doubt what the foreign keys are, i suggest you to read some books/articles before you actually start designing database. Databases are base for any project, and it is not something to be taken lightly