OK.So you want to put songs on a DSi,but you don't know how(duh).So,read below and i'll teach you how to put songs on a DSi(again,duh.)!Good Luck!
You'll need an SD card,an SD card READER!
Step 1:So,you got your SD card,right?Now put it in the SD reader and put that into the computer,open up the files
Step 2:Put a song you've downloaded on your computer and put that onto iTunes.
Step 3:Right-click on you're song on iTunes and select "convert selection into ACC" then wait when the song is done.
Step 4:Go into "recently added" on the sidebar and drag the song that you want(it HAS to be the top one!)on your Sd card in the folder "playlists"
If you want,you can make a new folder in the "playlists" folder(it doesn't have to be called a certain thing!Name it WHATEVER you want!)then drag the song in THERE!Perfect for organization!