I want to create a DBMS application using c.
For this purpose i need to know how to store data in different databases i.e. SQL, Oracle or MS Access.
It is ok if the data can be stored in the form of files but then the security of that files is issue.

You need a book on databases. Teaching that is beyond the scope of this forum.

ODBC is the oldest and most common way to access SQL databases with C and C++ languages. google for "odbc tutorials" and you will find some. You will also need to learn the SQL language. Although there is supposed to be a standard sql each database publisher implements its own little quirks. What works with one database may or may not work with others.