Understanding working of a DBMS

-- what happens when user enters a SQL request 
The client sends a SQL query to DBMS (which is installed in server), the client communicates with the DBMS with a communication protocol ODBC , JDBC
the request reaches the DBMS through various databse components which are present in the RAM and they are also interacting with the databsae files on disk 
-- above mentioned components :
listener - recieves incoming SQL queriesfrom clients and passes them to correct DBMS process
user process is initiated for each session(what s asessin , is it like individual request , such as select or the whatever queres have been passd in a particular time frame) that client makes to DBMS , 
the process basically consist of sending requests and recieving respinse and handling errors