Fir

When a complaint is given in a police station and police does FIR for that complaint, why does the police take the signature on the FIR from the complainant ?

and police also writes the summary of the complaint written by the complainant on the FIR does this should be exactly as written in the complaint,

i heard some weare that complainant should sign on the FIR only if FIR is wright, how does the comman man know weather FIR is wright or wrong.