Q: how do I download my songs

Download what songs and to what ? If you want to redownload your past purchases to your computer's iTunes then you might (depending upon what country that you are in and if the music is still in your country's store) be able to redownload them via the Purchased link under Quicklinks on the right-hand side of the iTunes store homepage. If you can't redownload them then you will need to copy them form your backup of your library.

If they are pre-ordered songs that are now available then try the Store > Check For Available Downloads menu option on your computer's iTunes.

If you mean something else ... ?