how to use niosII ide

The Nios IDE is a tool to write "software" that can run on the NIOS (a soft-core processor inside an Altera FPGA).

The code you have in VHDL is synthesizable into Altera FPGA gates, and produces "hardware" structures.

There is no way to automatically translate "hardware structures" (VHDL) into "software" that runs on a processor inside an FPGA.

And even if such a tool would be available it would be highly unefficient.

What is very efficient is to combine a NIOS with VHDL. Then you get efficient code (VHDL) with the flexibility of software on top; the best of both worlds.

So please read some more documentation so that you can find out what you really want and need.