Cathy,
Copying music files onto the phone is easy. I have a Galaxy S3 and I do the following:
1. Turn off the phone and take out the Micro-SD card where my phone stores camera pix, videos and also my music.
2. Insert the card into an adapter that plugs into a USB port on my computer. Plug it in and wait until the card shows up as an external drive. Works on a Mac as well as on a PC.
3. On the computer, find the folder where your music is kept. As long as your music is in .mp3 format, it will play on the Android phone.
4. Simply copy the music files you want from your computer to the SD card, just like if you were copying files from hard drive to another. You can copy whole folders, keeping your filing system intact.
5. Unmount the SD card from the computer, put it back in the phone, close the cover, turn the phone back on.
It will take a little bit for the phone to find and catalog the new media. But in the end you will have music library on your phone sortable by title, artist, album, genre etc. my problem is that my SD card is 64 gb, but my music library about 150 gb, so I have to be selective, which music I put on the phone.
6. Easy so far. Playlists will more tricky. I too have many playlists that have taken me years to assemble. I don't bother moving them to the phone, but I suppose it could be done. Playlists can be saved as .m3u files (simple text files that list sequentially the media files to be played). If these can be created on the Computer side, they could certainly be copied to the SD card, but the question is whether Android will know what to do with them. There may be a way to somehow make this work. Comment from another CNET user, please?
Good luck,
Radim