nios II processor interface with memory

You must use C code with the nios cpu, not vhdl.

When you generate the bsp you will have a system.h file with some defines. One of them will be the name of your memory, with _BASE appended to it. This is the base address of the memory area, and you can use it to set the address of a C pointer. Then just use the pointer to read/write values in the memory.

You can connect as many memories as you want to the CPU, as long as you have enough room in the FPGA for all of them.