How to make a class Library containing following things

Question

I am given a requirement where i have to make a class library file and write a function called executeDML in that and inside that function i have to write all the DML statements like Insert,Delete and when in some other file i write a DML statement it should get executed through 1st file where executeDML() function is there and that function should contain code that decides whether the DML query to be executed is Insert or Delete and then it should execute that query only.
                                     In short my 1st class library file that contains executeDML function also contains other functions like getConnection() that contains connection part and 1 more function that will get all the values from database.This file is then used by all other files for connection or for execution of queries.
                                 Please someone help soon.