Electrical – MIPS: Instruction Memory: Referring to instruction in memory

I'm implementing MIPS processor using Verilog.

input   [31:0] address;
output [31:0] instruction;
reg [31:0] instruction_memory [255:0];
assign instruction = instruction_memory[address[9:2]];

This is an almost complete body of Instruction Memory module.
The thing I cannot understand is why we refer to the instruction in memory using address[9:2]. I mean, why [9:2] ?

I've found an answer, but I cannot understand it. It says:

What bits select the first 256 words? [9:2]!

Can you, please, explain me this detail in some other, more understandable way?
Thank you.