How do i implement speech recognition in verilog using nexys4 ddr development board?

I suggest you stick to Intel FPGA issues on an Intel forum...

First of all, the Nexys4 board uses a Xilinx FPGA.

As for development steps:

1. Develop the speech recognition algorithm (probably in matlab or C)
2. Then write the verilog code in some text editor
3. Verify the verilog against your reference model
4. test it on the board.