Assuming you're referring to files like MP3s and Photos, the easiest way is to locate the files on your PC then drag and drop them onto your Droid.
As an IT-pro, I of course have zero idea how you do that on a MAC
, however on a PC, your music will be under your My Music
folder in a sub-folder called something like iTunes
(this is all from a very poor memory
). Easiest way to find it is to search under My Music
for *.MP3 (and any other suffices you may have like *.MP4).
I have no idea where photos are stored, but I'm guessing somewhere the same folders structure. Easiest way to find them would again be to use Search for *.JPG.
Note that how you search depends on the version of Windows you're running: on XP, there's a specific tool, on Win7 (and I guess 8) you can just type in the search box in the top left hand corner of Windows Explorer.
To drag and drop the files to your 'droid you just need to connect the droid via USB and use Windows Explorer.