You need to use iMovie. I'm not sure why people are saying iPhoto, unless I'm missing something...and I've used a Mac for YEARS. That's the whole purpose for iMovie! You don't even need to upload your pix into iPhoto, if you have the latest version. Just make a folder on your desktop and drop all you pix in them. You can drag your pix straight from the desktop into iMovie with the latest iMovie version. Very nice! Download your music from iTunes or a CD and drag the music you choose under the pix you want it to be with on the movie. The new iMovie even has themes that will practically make the movie for you and it adds all the transitions as well. Have fun playing with it!
Good luck!