The Supervisor of Elections shall prepare full instructions for the guidance of voters at primaries and general elections, as to obtaining ballots, the manner of marking them, the method of gaining assistance, and as to obtaining new ballots in place of those that are found to be unserviceable or are accidentally spoiled; and shall cause such instructions to be printed in clear type, on separate cards, to be called cards of instruction; and he shall furnish to each board of elections a suitable number of such cards for each polling place in its district.