how do i send songs i bought at the istore to my new ipod nano 16gb?

You should be able to connect the iPod to your computer and select it on the left-hand sidebar of your computer's iTunes (if you have iTunes 11 on your computer then you can enable the left-hand sidebar via control-S), and then use the Music tab on the right-hand side of iTunes to select and sync the songs to it.

Syncing music :http://support.apple.com/kb/HT1351

See page 15 of the iPod nano User's Guide:

http://manuals.info.apple.com/en_US/ipod_nano_user_guide.pdf

You may also find this support article helpful:

http://support.apple.com/kb/HT1386

Though it is mostly applicable to an iPod touch, not a nano, the section on synching via USB may still be of help since it includes screen shots.

Regards.