Register file has four inputs: Port1 datain, Port2 datain, Write enable and Write Address. It gives out four outputs: Port1 dataout, Port2 dataout, Port1 Z out, Port2 Z out
There are 32 (0..31) 32-bit registers in the register file. If you want to read from a particular register, all you need to do is set the address input to the address of that register and the data read from that register should be output at the appropriate pins shown in above schematics. Writing to a register involves setting WERF to Non Serialzed High, setting appropriate address and appropriate data. Register file also outputs a serialzed one at Z output if the value read from that register is 0.