Please help me ......SDRAM DE2

Mmm there is some confusion here: you first state that you want to access SDRAM memory using C, but later you state you want to access from a custom IP.

I will try to be more clear, what you need to do is:

A) Interface a VHDL/Verilog hardware module you have developed to a SDRAM memory?

B) Develop software in C code just like you would do in any microcontroller/microprocessor and take advantage of SDRAM as main program memory?