If you're interested in the importance of accommodation of entity relational diagrams to relational schema then the following pre-existing Blurtit question may be of use to you:
To add some additional resource information though, I would say that a broad definition of the process you are seeking explanation for would be "an attempt at charting out the ER entities and relationships that exist in the real world, and then transferring them into the context of a database, so that relationships and bonds become evident.
I also found the following powerpoint presentation highly relevant to this topic: www.cs.toronto.edu/~ryanjohn/teaching/cscc43-s12/lectures/c4