i created a new folder on my SD card called 'others' and i just put the .apk files in there so i know where to find them all easier with my file manager.
if your new to smartphones you will perhaps need to know that the SGS2 treats the internal memory like an SD card so for the actual SD card you can remove, if you have one, is noted in the file manager as external sd card
but that doesnt matter so much, just create a new folder and put them in so you'll know where to be looking.
the usb cable will probably be the easiest way, your phone will pop up with something when you plug it in and you can select usb storage