Help me for connection

I'm confusing about parallel and serial connection. I have 2 pairs of speakers and want to connect them to amplifier. If I connect all speakers to binding posts of amplifier then what is it ? Parallel or serial connect ? If I connect a pair of speakers to amplifier and then connect the other pair to the first pair then what is that ? Which one is better ? And does amplifier see any difference of impedance of speakers between parallel or serial connnect ? My speakers are 4 Ohm load pair and 6 Ohm for the another. And where can I find more information about that ? Thank you very much guys.....