Hi Roopa,
You have to go through Nios II Processor Reference Guide, Nios II Software Developer Handbook or go through the online training. Refer below links
https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/nios2/n2cpu-nii5v1gen2.pdf
https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/nios2/n2sw_nii5v2gen2.pdf
For online training click below link and search for Nioss in the search box, you can find courses like Nioss II hardware, Software & Custom component and instruction development
https://www.intel.com/content/www/us/en/programmable/support/training/catalog.html
Regards
Anand
