It's basically how you want to play the game.
For the .swf files you just need to download a flash projector from the Adobe site. AIR versions use Adobe AIR instead. Couldn't tell you on APK files though.
Imagepacks are just that, much larger files that contain the game and full res images instead of profile pics.
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Please note, while this is a link to the Adobe site, I do recommend searching it for yourself and going that way. General internet safety and all. If you search adobe flash projector you'll end up in the same place, just not hotlinked from F95.
Basically, you'll want to download the "Flash Player Projector" midway through the Windows downloads, assuming you are using windows. Download a .swf of your choice (imagepacks are best IMO, but 3-400mb instead of 75mb or so for regular versions) and away you go.