What does the verilog code 2'b0001 mean? As in how many bits is it, what's the number associated with it, and what base is it in?

What does the verilog code 2'b0001 mean? As in how many bits is it, what's the number associated with it, and what base is it in? Can you also explain the general format of Verilog code so that i can identify what a given code means?