Nios II basic

U have to build the FPGA system using SOPC/QSYS , the NIOS code to interact with the FPGA will have to be done using eclipse

for ex : to transfer data from NIOS Console to DDR.

U will have to create a system onchipmemory-DDR controller-DMA etc using SOPC/QSYS and synthesize to get an .sof

then ur code to sent data to the write /read to the DDR will be a .c file which you have to build using eclipse and get an .elf

U can flash both .sof n .elf and they would do the respective work.