what does Import User and Role Application Security Data Process do behind the scene?

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Security gurus,

Can someone explain what does the "Import User and Role Application Security Data Process" process actually does behind the scene? Also, when Oracle says it's an LDAP synch you run prior to implementation, I assume it is connecting to an internal Oracle directory (as oppose to, connecting to client's AD which requires additional setup)?  Any additional explanation to the behind the scene Oracle architecture and what this process does and why one needs to run it, will be very helpful.