Please got to publish+share, there you can select the option to export.
And then you can upload it onto YouTube.
Or you can directly upload video onto YouTube by selecting the option "Social Websites"
Given you have Premiere Elements 12/12.1. (limit...2 GB 15 minutes, even if you have an extended time account at YouTube...the extended time account applies only to file uploaded to YouTube at the YouTube web site)
If your goal is to get a Premiere Elements 12 Timeline uploaded to YouTube, you have two possible routes....
a. Publish+Share/Social Websites/YouTube and your selection of the preset that matches your Timeline properties
b. Publish+Share/Computer/AVCHD with one of the .mp4 preset to export the Timeline content to a file saved to the computer hard drive from where you upload it to YouTube at the YouTube Web site.
For best results, I would suggest an AVCHD.mp4 file instead of the "avi" that you mentioned. What is the video compression that goes with that "avi" wrapper?
As for .mp3, that is a audio file extension, what is your intent on that....an upload to YouTube with just music and with a black video display? YouTube strictly enforces any copyright issues, so please assure that there are none associated with these .mp3 otherwise YouTube will remove them.
Please review and consider, and then let us know if you have the information that you sought.