How can I transfer my mp3 tunes from desktop PC to iPhone? I tried copying files manually, but it doesn't seem to work.
In order to copy mp3 files from PC to iPhone you need to use iTunes.
After connecting your iPhone and starting iTunes the phone should be visible in the list of synced devices. Now select and drag the mp3 files you want to transfer to the area in iTunes where the connected iPhone is listed. Your music mp3's will be converted to iPhone format and copied onto the device.
Please note that file names of the mp3 tracks may change when transferred to iPhone.
Before syncing your mp3's with an iTunes connected phone please make sure that you've authorized the computer to be used with iTunes. To do so, login to AppleID and authorize the computer. Otherwise the sync process will fail.