DRM is Digital Rights Management, a weird encryption thing that Apple did for a few years. As far as the sequence to create a ringtone from your own music, the following is the sequence for a PC. Apple computers make it easier, and I'll go over that after the PC directions.
1. Start iTunes and find the song you want to convert. (It must be an MP3.)
2. Right-click the song and choose Get Info.
3. Click the Options tab.
4. Check the Start Time and Stop Time boxes, then enter times for each (no more than 30 seconds apart, the maximum length for a ringtone). I use the very beginning of The Spicy McHaggis Jig, as it has loud annoying bagpipes and is super noticeable.
5. Click OK, then right-click the song again and choose Create AAC Version. You should immediately see a new 30-second version of the song.
6. Drag that version out of iTunes and into the folder of your choice.
7. Delete the 30-second version from iTunes and undo the Start Time/Stop Time changes to the original.
8. Open the folder containing the 30-second AAC file you dragged out of iTunes, then change the file extension from .m4a to .m4r. Double-click it and it immediately gets added to iTunes' ringtone library.
9. Finally, sync your iPhone. When it's done, you can head into the settings and select your new ringtone.
how to turn file extension changing on (do this either before doing anything, after creating a folder with your ringtones, or at least before step 6 in the above list.
1. find the folder that you dragged the file into from step 6 above
2. Click the dropdown box that says "organize"
3. Click on the option that says "folder options"
4. click on the tab that says view
5. un-select the option "hide extensions for known file types" "
For Apple computers it's really easy, takes a few steps, but after you’ve done it a few times it’s not bad at all:
1. Open iTunes
2. Find the song you want to make into a ringtone.
3. With two fingers, click on the trackpad (or whatever it's called on Apple computers)
4. Select "Get Info"
5. Mark the start time and end time checkboxes with the part of the song you want to use for a ringtone (30 second or less clip)
6. Click back into the regular iTunes screen
7. Two-finger click the song again and select “Create AAC Version”
8. Click and drag the file from your itunes screen to wherever you want to store your ringtones
9. Delete the file from itunes, but not from your computer when prompted
10. Two Finger click the file in the folder you have it stored in (In Finder) and select “Get Info”
11. Go to where it says “Name and Extension” and change the name to whatever you want it called in your list of ringtones, but change the extension from .m4a to .m4r, select the button that says “Use .m4r” when prompted
12. Open the file, and it will be added to your available ringtones, make sure you select the option when syncing the iPhone that syncs ringtones too, third tab from the left when you have the phone plugged in
13. Go back to the original version of the song that you turned into a ringtone in iTunes, and deselect the “Start Time” and “End Time” boxes so you don’t have a 30 second clip of the song when you want to listen to the song normally
14. Sync your iPhone, after which the ringtone will be available to select instead of fricking Marimba or something