To Export it, click on 'Share' at the top, then pick what you want to share it too. iDVD will work best for a regular DVD player, but you may need to mess with it a bit if you haven't used it before, just to get used to setting up the menus and all.
To Export it to .avi, select to share to Quicktime, then in the dropdown menu that comes up select Expert Settings.
Click the Share button, and it will ask for a filename and location to save it too, then just below that in the same window, you can select what format to save it as...AVI should be in the list, you can also click the options button after that to set Screen resolution, audio, etc.
Best,
Brian