Hi TMahoney1979,
Welcome to the Apple Support Communities! It sounds like you are asking two questions here, so I'll provide resources for both.
Make a Backup Copy of the iTunes Library on an external drive
If you want to make a backup of your iTunes Library on an external drive, the resource below will show you how.
Manage and back up your iTunes media library
Convert all songs in iTunes Library to MP3 format
If you want the backup to be all of your songs in MP3 format, then you would first have to convert all of the songs in your iTunes Library to MP3, and then copy those files to an external disc. This would create a copy of your music on the external drive, but not the features (playlists, etc.) that you have in your iTunes Library. This process also will create a second copy of the song in your iTunes library, so you would have to go through and delete the version of the song that you don't want in iTunes. IMPORTANT: Make a backup of your iTunes Library (see above) before making this change to it.
Convert a song to a different file format with iTunes
I've highlighted some key information from the resource for you below. Click on the link for complete details.
* Note: In step 7 below, if you want to include all of the songs in your iTunes Library, then the folder you would choose to convert is Music > iTunes > iTunes Media > Music
You can import songs into iTunes and convert them at the same time. This creates a converted copy of the file in your iTunes Library, based on your iTunes preferences.
To convert all of the songs in a folder or on a disk:
- Open iTunes.
- Mac: From the menu bar at the top of your computer screen, choose iTunes > Preferences.
Windows: From the menu bar at the top of the iTunes window, choose Edit > Preferences.
- Click the General tab, then click Import Settings in the lower section of the window.
- Click the menu next to Import Using, then choose the encoding format that you want to convert the songs to.
- Click OK to save the settings.
- While holding down the Option key (Mac) or Shift key (Windows) on your keyboard, choose File > Convert > Convert to [import preference]. The format shown is the one that you chose in step 4. For example, if you chose Apple Lossless Encoder, select Convert to Apple Lossless.
- Select the folder or disk that contains songs that you want to import and convert. iTunes converts all of the songs in the folder or on the disk.
The songs in their original format and the converted songs appear in your library.
Older purchased songs are encoded in a Protected AAC format that prevents them from being converted. Learn how to upgrade these and then convert to another format.
Once all of the songs have been converted, you can use the Finder application to find all of the MP3 files on your computer and copy them to a folder on an external drive. Or, you can select all of the MP3 files from withing iTunes and drag them to a folder on your desktop, then to an external drive.
Have a great day!